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Pitch (Asphalt) Lakes of Trinidad, Venezuela, and California
A pitch lake is a deposit of natural asphalt in a “great expanse of more or less mobile character, covering many acres, and resembling in many ways a similar expanse of water”, said petroleum geologist Clifford Richardson in 1917. (1) The most classic of all pitch lakes is Trinidad Lake in the Caribbean West Indies’ Island of Trinidad, but other pitch lakes exist throughout the world, including the Bermudez Lake in Venezuela, and the Rancho La Brea “Tar” Pits in Los Angeles, California. The meanings of the related terms asphalt, petroleum, bitumen, pitch, tar and hydrocarbons, are continuously evolving. Their meanings emanate from certain times and places, for example, the Roman era of “bitumen” and the modern era of “petroleum”. Even the term lake, as applied to natural asphalt deposits, may overstate the reality of these often soggy, belching, smelly, weeping sores of the Earth’s crust. I. Meaning of “Asphalt” Early geologists, such as Henry William Bristow in 1861, who described naturally occurring asphalt in asphalt mines and asphalt surface deposits, described it as a solid and opaque mineral with a velvet-black or sometimes a brownish black color. (2) 
Asphalt mine in Neuchatel, Switzerland. Source:
http://www.villamoncalme.ch/moncalme/img/Minesasphalte(B).jpg; accessed December 10, 2007. 
Asphalt consistence, Trinidad pitch lake. Source:
http://www.jaunted.com/tag/Lake; accessed December 10, 2007. He also noted that asphalt shines with a resinous luster, breaks with a brilliant conchoidal fracture, feels greasy and emits a “bituminous” odor when rubbed, burns with a bright light and a smoky flame (leaving a small quantity of ashes), has a specific gravity of 1 to 1.2, and fuses at 100 degrees Centigrade (212 degrees Fahrenheit). Bristow noted the chemical composition of an asphaltum (a synonym of asphalt) from the island of Brazza (now called Brac), in Dalmatia (modern Croatia), as follows: petrolene (volatile oil), 5.0%; brown resin, soluble in ether, 20.0%, asphaltene (bitumen soluble in alcohol and ether), 74.0%; yellow resin, soluble in alcohol, 1.0%; for a total 100%. (2) Discoveries in petroleum refining, which began in earnest in places like Baku, Azerbaijan, under the aegis of Robert Nobel and other entrepreneurs in the late 1800s, as described elsewhere, led to the finding that asphalt originates from petroleum during the crude oil refining process. (3,4) Petroleum geologist Speight notes asphalt produced in this manner can resemble “bitumen”, hence the tendency to call bitumen “native asphalt” (more on bitumen below). Calling bitumen “native asphalt” is an incorrect use of terms, Speight declares, and recommends that the term asphalt, as currently used and understood today, refer only to manufactured asphalt, i.e., that produced by the refining of “petroleum”. Historians of asphalt roads, which were first laid down in Europe and in the United States in the second half of the 19th century, will note, however, that the asphalt came not from manufactured asphalt, but from natural asphalt deposits excavated mostly from the La Presta mine in Neuchatel, Switzerland, and Lake Trinidad. II. Meaning of “Petroleum” The term petroleum means literally “rock oil”. It is “a myriad of hydrocarbon-rich fluids that have accumulated in subterranean reservoirs”, notes Speight, who continues, “Petroleum, also known as crude oil, varies dramatically in color, odor, and flow properties that reflect the diversity of its origin. Petroleum products are any products obtained by refining petroleum, and include refinery gas, ethane, liquefied petroleum gas, naphtha, gasoline, aviation fuel, marine fuel, kerosene, diesel fuel, distillate fuel oil, residual fuel oil, gas oil, lubricants, white oil, grease, wax, asphalt, and coke.” [Bolding added.] (5) These products are “highly complex chemicals, and considerable effort is required to characterize their chemical and physical properties with a high degree of precision and accuracy...Crude petroleum and the products obtained therefrom contain a variety of compounds, usually but not always hydrocarbons. As the number of carbon atoms in, for example, the paraffin series increases, the complexity of petroleum mixtures also rapidly increases. Consequently, detailed analysis of the individual constituents of the higher boiling fractions becomes increasingly difficult, if not impossible.” (4) Marine microbiologist Claude E. ZoBell, who worked at the Scripps Institution of Oceanography of the University of California, La Jolla, said in 1945, “In view of the ever-increasing importance of petroleum and its myriads of products to our mechanized and martialized civilization, it seems anomalous that our knowledge of what petroleum is and how it is formed is still so woefully wanting. Petroleum geologists have been so successful in finding subterranean deposits and the industry has been so efficient in providing almost any required amount of amazingly low-cost petroleum products that no one has been too much concerned about what petroleum is or how it was formed.” (6) ZoBell’s microbiology background informed his particular view of petroleum, which he defined as follows: “A complex mixture of gaseous, liquid and solid hydrocarbons. Besides the uncounted hundreds of hydrocarbons composing petroleum, there are numerous compounds of hydrogen and carbon which contain oxygen, nitrogen, phosphorus or sulfur. Petroleums from different oil fields differ widely in chemical composition and in physical properties. Some crude oils such as those from the Bradford, Pennsylvania, sands, for example, are clear amber-colored, free-flowing fluids, while others, exemplified by La Brea, California, crudes, are coal black, viscous tars…The range in the chemical composition of petroleums is as follows: Carbon, 82.2 to 87.1%; Hydrogen, 11.7 to 14.7%; Sulfur, 0.1 to 5.5%; Nitrogen, 0.1 to 1.5%; Oxygen, 0.1 to 4.5%; and Minerals, 0.1 to 1.2%. The hydrocarbons in various petroleums may consist predominantly of either (1) aliphatic compounds of the paraffin series, (2) aromatic compounds of the benzene series or (3) naphthenic compounds of the polymethylene or cyclo-paraffin series. Likewise found in various crude oils are small quantities of fatty acids, phenols, naphthenic acids, resinous compounds, asphaltenes, mercaptans, thiophenes, sulfones, sulfoxides, sulfonic acids, organic sulfides, pyridines, quinolenes and other compounds. So complex are petroleums and so labile are some of their constituents that no crude oil has ever been completely analyzed. [Italics added.]” (6) III. Meaning of “Bitumen” The Romans invented the term bitumen to describe naturally occurring hydrocarbons mixed with varying amounts of sand, crushed limestone, or some other mineral material such as clay. (1) Speight, by contrast, sharply defines bitumen as “that portion of petroleum, asphalt, and tar products which will dissolve completely in carbon disulfide (CS2). This property permits a complete separation from foreign products not soluble in carbon disulfide.” (7) Speight also notes that bitumen is frequently found in the crevices of sandstone, limestone, or argillaceous sediments, in which case the organic and associated mineral matrix is known as rock asphalt.” Bitumen, he continues, “is also a naturally occurring material that is found in deposits that are incorrectly referred to as tar sand, because tar is a product of the thermal processing of coal.” (8) In Europe today, however, asphalt is commonly known as bitumen, according to Asphalt (Bitumen) (Concise International Chemical Assessment Document (No. 59), published in 2004 by the World Health Organization, which monitors the effects of asphalts on human health and the environment. (9) The WHO authors continue, “Asphalt is dark brown to black, cement-like semisolid or solid or viscous liquid produced by the non-destructive distillation of crude oil during petroleum refining...Performance specifications (e.g., paving asphalts and roofing asphalts), not [italics added] chemical composition, direct asphalt production. The exact chemical composition of asphalt is dependent on the chemical complexity of the original crude petroleum and the manufacturing process. “Crude petroleum consists mainly of aliphatic compounds, cyclic alkanes, aromatic hydrocarbons, polycyclic aromatic compounds, and metals (e.g., iron, nickel, and vanadium). The proportions of these chemicals can vary greatly because of significant differences in crude petroleum from oil field to oil field or even at different locations in the same oil field. While the manufacturing process may change the physical properties of asphalt dramatically, the chemical nature of the asphalt does not change unless thermal cracking occurs. Although no two asphalts are chemically identical and chemical analysis cannot be used to define the exact chemical structure or chemical composition of asphalt, elemental analysis indicate that most asphalts contain 79-88 wt% carbon, 7-13 wt% hydrogen, traces to 8 wt% sulfur, 2-8 wt% oxygen, and traces to 3 wt% nitrogen. [Italics added.] (10) IV. Meaning of “Pitch” Speight argues, “[It] is incorrect to refer to native bituminous materials as tar or pitch. Although the word tar is descriptive of the black, heavy bituminous material, it is best to avoid use with respect to natural materials and to restrict its meaning to the volatile or near-volatile products produced by the destructive distillation of such organic substances as coal. In the simplest, sense, pitch is the distillation residue of the various types of tar.” (11) “Pitch”, according to Webster’s International Dictionary of the English Language (Second Edition, 1941) derives from various Greek, Latin, and other language roots that mean “moisture”. Webster’s definition #1 states pitch is “a black or dark-colored viscous substance obtained as a residue in distilling coal tar, wood tar, petroleum, bone oil, fixed oils, etc., and occurring naturally as asphalt. [Italics in original.] Artificial pitch, like asphalt, consists chiefly of hydrocarbons, but varies much in composition and consistence according to the way it is produced. Thus, that from wood tar is hard and brittle; that from coal tar may be either hard or soft. Pitch is widely used in manufacturing fuel, varnishes, roofing paper, etc., for calking seams, as a preservative coating, as a lubricant, in insulating, for street paving, etc.” Definition 2 states that pitch is “any of various bituminous substances; sometimes with a limiting word; as mineral pitch; Jew’s pitch.” [Italics in original.] Definition 3 states pitch is “the resin, often of medicinal value, obtained from certain coniferous trees; as, Canada, or hemlock, pitch; etc.” V. Meaning of “Tar” Tar is “a thick dark brown or black, viscous liquid obtained by the distillation of wood, coal, peat, and other organic materials, and having a varied compositions according to the temperature and material employed in obtaining it”, says Webster’s International Dictionary of the English Language (Second Edition, 1941). A second definition of tar provided by Webster’s is any substance resembling the substance defined in definition 1, in appearance, formed by chemical change. Note that the naturally occurring La Brea “Tar” Pits in Los Angeles, California, contain asphalt, not tar, and are more accurately called “asphalt pits”. VI. Meaning of “Hydrocarbons” Hydrocarbons are chemical compounds composed of carbon and hydrogen molecules. The majority of hydrocarbons found naturally occur in crude oil, where, according to one theory, decomposed organic matter buried in sediments over hundreds of millions of years has provided an abundance of carbon and hydrogen which, when bonded, can catenate to form seemingly limitless chains. An alternative theory of the origin of Earth’s hydrocarbons, held by the late Thomas Gold and other geophysicists, especially in Russia and China (as described elsewhere) is that hydrocarbon substances in the Earth’s crust were “brought in from space when the Earth was formed.” (12,13) “When asked what first prompted him to think that oil and natural gas are generated from hydrocarbons present at Earth’s formation, Gold replied, ‘The astronomers have been able to find that hydrocarbons, as oil, gas and coal are called, occur on many other planetary bodies. They are a common substance in the universe. You find [large quantities of hydrocarbons] in the kind of gas clouds that made systems like our solar system...Is it reasonable to think that our little Earth, one of the planets, contains oil and gas for reasons that are all its own and that these other bodies have it because it was built into them when they were born?’” (12) “When the interviewer replied, ‘That question makes a lot of sense. After all, they didn’t have dinosaurs and ferns on Jupiter to produce oil and gas,’ Gold said, ‘That’s right. Yet, for some reason my theory was not heard. The theory that it was all made from fossils ha[s] become so firmly established that when the astronomers had perfectly definitive evidence on most of the other planets, it was just ignored, especially by the petroleum geologists who had, by then, called these things, ‘fossil fuels.’ So once they had a name, then everybody believed it.’” (12,13) VII. Trinidad Pitch Lake The Island of Trinidad lies “off the north coast of South America, between 10 degrees and 11 degrees of latitude and 61 degrees and 62 degrees longitude. On its north is the Caribbean Sea; on its east the Atlantic Ocean, on its south a narrow channel into which flow the waters of the northern and most westerly mouths of the great Orinoco River, which drains Venezuela; and on its west the Gulf of Paria. (1) The island’s shape is irregularly rectangular, about 48 miles in length and 36 miles in width, for an area of about 1,750 square miles (about one-fifth the size of the state of Vermont). (1) Promontories jut off its southwestern and northwestern corners, which are several miles in length and reveal that structurally, Trinidad is in reality part of the South American mainland.  Arrow points to Trinidad and Tobago Islands, just off the coast of Venezuela, near the mouth of the Orinoco River. Source:
http://www.localization-translation.com/globalization-guide/localization-countries/localization-trinidad-tobago.html; accessed December 10, 2007. 
Map of Trinidad. Source:
http://www.gstt.org/teaching/piparo_mud_volcano.htm; accessed December 10, 2007. 
Geologic map of Trinidad Island. Source:
http://www.gstt.org/map/kugler_1959_geological_map.htm; accessed December 10, 2007. Sir Walter Raleigh sailed to Trinidad in 1595 AD and wrote about what Amerindians called Piche and the Spaniards called Tierra de Brea (brea in Spanish means tar): “From thence I rowed to another port, called by the naturals Piche, and by the Spaniards Tierra de Brea. At this point, called Tierra de Brea or Piche, there is that abundance of stone pitch that all the ships of the world may be therewith laden from thence; and we made trial of it in trimming our ships to be most excellent good, and melteth not with the sun as the pitch of Norway, and therefore for ships trading the south parts very profitable. From thence we went to the mountain foot called Annaperima...” (14) Clifford Richardson wrote in 1917: “The island is remarkable for the occurrence of bitumen in characteristic forms, as an asphaltic petroleum, as grahamite and as a solid bitumen or asphalt associated with mineral matter in the so-called lake.” (15) He further noted that scattered over the island were many deposits of asphalt, but the one of commercial importance, the pitch lake, lay on the southwestern promontory mentioned above, at the highest elevation (138 feet above sea level). Between the pitch lake and the sea were other deposits, covered more or less and mixed with soil. The names of the pitch from the lake and the land were “lake pitch” and “land pitch”, respectively, he said.  Map of Trinidad showing oil deposits. Source:
http://www.gstt.org/Geology/bibliography.htm; accessed December 10, 2007. 
Aerial map of Trinidad pitch lake. Source:
http://www.gstt.org/Geology/pitch%20lake.htm; accessed December 10, 2007. 
Kugler map of Trinidad pitch lake (1959). Source:
http://www.gstt.org/Geology/pitch%20lake.htm; accessed December 10, 2007. The Trinidad pitch lake is nearly circular in diameter, with an area of some 115 acres, and looks from an aerial view like a huge methane or other gas blowout hole. The ground falls away from the lake on all sides, and “it seems plain that this deposit lies in the crater of a large mud spring which has filled up with asphalt.” (15) Geologists determined with borings through the asphalt in 1894 that the depth of the lake at the center was 135 feet. (16) The asphalt at the surface of the lake was the same as the asphalt at the bottom of the lake. “The pitch lake…is a bowl-like depression, more than 2000 feet across, and over 135 feet deep, reaching to the sea level, and filled with a uniform mass of asphalt, a mass which must amount to many millions of tons, making it the largest deposit of solid native bitumen in the world,” declared Richardson in 1917. (16) Subsequent geologists would disagree with Richardson’s characterization of the lake as “bowl-like” (more below). Bristow in 1861 described the pitch lake as follows (2): “The Bitumen is solid and cold near the shores, but gradually increases in temperature and softness towards the centre, where it is boiling. The solidified bitumen appears as if it had cooled as the surface boiled, in large bubbles. The ascent to the lake from the sea, a distance of three-quarters of a mile, is covered with a hardened pitch, on which trees and vegetables flourish; and about Point La Braye (La Brea), the masses of pitch look like black rocks among the foliage. The lake is underlaid by a bed of mineral coal (Manross, quoted by Dana). The Pitch Lake of Trinidad, according to Mr. G. P. Wall, yields three kinds of asphaltum, viz:
Richardson in 1917 continues on the same theme, “The surface of the main deposit or lake contained in the crater is not a uniform expanse of asphalt, or pitch as it is called locally. It is grassy along the edges and becomes free from vegetation at some distance from the center. Shrubs and small trees occur in few cases known as islands. These patches move from place to place with the movement of the pitch. The main mass is a broad expanse of asphalt made up of separate areas of irregular outline, but at times quite circular, which are separated by channels, filled with rain water, which prevents their coalescence. The boundaries are depressed and the center of the areas is always somewhat elevated above the edges, that is to say, they are mushroom-like. “The origin of the separate areas evidently lies in the constant movement of the crude material, due to the evolution of gas at the center, from which point the asphalt rolls over toward the edges. This is shown by the fact that pieces of wood which emerge erect at the center are gradually carried to the circumference, their deflection form the perpendicular increasing as the distance from the center increases. At the channel they topple over and are again engulfed. This illustrates very well the activity of the entire deposit, although it is much more active near the center of the lake.” (16) Richardson noted that a hole dug in the surface of the pitch lake rapidly filled up, repairing the surface to its original level after a short time. Workers are able rapidly to flake out the pitch with picks in large conchoidal masses, each weighing between 50 and 75 pounds. Each chunk, according to Richardson, was honey-combed with gas cavities, and resembled in structure a Swiss cheese. The temperature of the pitch at the surface was not greater than that of the surrounding air except when it was exposed to the noon-day sun, when it sometimes rose to 130 degrees Fahrenheit or greater, he noted. (17)  Trinidad pitch lake. Source:
http://www.richard-seaman.com/Travel/TrinidadAndTobago/Trinidad/PitchLake/index.html; accessed December 10, 2007. 
Cross section of Trinidad pitch lake. Source:
http://www.gstt.org/Geology/pitch%20lake.htm; accessed December 10, 2007. 
Cross section of Trinidad pitch lake. Source:
http://www.gstt.org/Geology/pitch%20lake.htm; accessed December 10, 2007. In the center of lake, the emanating gas consisted mainly of methane with a considerable proportion of carbon dioxide, observed Richardson. The influx of soft material at the center of the lake, however, evolved gas of quite a different character, containing a large percentage of hydrogen sulphide (H2S, smells like rotten eggs). Indeed, the bitumen of Trinidad asphalt contains 6.16% sulphur (a relatively high amount), 0.81% nitrogen, 10.69% hydrogen and 82.33% carbon, said Richardson. (17) He also measured the components of the asphalt pitch: water and gas, volatilized at 100 degrees Centigrade, 29 crude percent; Bitumen soluble in cold carbon disulphide, 39 crude percent; Bitumen absorbed by mineral water, 0.3 crude percent; mineral matter, on ignition with tricalcium-phosphate, 27.2 crude percent; and Water of Hydration in clay and silicates, 4.3 crude percent. (17) So much free water accompanies the asphaltum in the lake, observed Richardson, one can roll some into a ball without it adhering to one’s hands. “The softer asphalt [i.e., nearer the center of the lake] is in an active state of change, since if it is sealed in a tin can the gas evolved will, in a few weeks, burst the containing vessel,” he continued. (17) When samples were pulverized and dried in the air at ordinary temperatures, to free it from the water, the average composition was around 55% Bitumen CS2, Mineral Matter, 35%; and Water of Hydration 10%.) To summarize, Richardson noted, ‘The crude asphalt, therefore, consists of an emulsion of water, bitumen, fine silica and colloidal clay, the latter playing an important role in producing a bitumen of desirable character for paving purposes.” Furthermore, “The percent of soluble mineral matter or salts present in the asphalt as compared to that of the bitumen is extremely small and unimportant, and plays no part in the behavior of the material industrially, since the addition of the same salts to other asphalts has been found to produce no perceptible effect upon them.” (18) VIII. Recent Geologic Investigation of Trinidad Asphalt Lake In November 1989, geologists with the Geological Society of Trinidad and Tobago re-investigated the Trinidad asphalt lake “(i) to determine the geometry and depth of the asphalt lake, (ii) to determine from density contrasts, the type of rock beneath the Asphalt Lake, and (iii) to determine the possible source or sources of asphalt in the lake.” (19) They found that a gravity low exists at the present lake and trends NNW-SSE. The lake is not bowl-shaped as previously thought (see above), but irregular, with a possible plug at the center. The modeling of the lake showed that two, possibly large faults exist, which are connected to the Los Bajos fault system to the south. “These two faults intersect at the asphalt outcrop and the asphalt is sourcing from them.” (19) The implication here is that hydrocarbons from the deep hot bio-geosphere are extruding into the asphalt lake through cracks in the Earth’s crust, i.e., earthquake faults. IX. Bermudez Pitch Lake, Venezuela The mouth of the Orinoco River on the northeastern coast of Venezuela, faces Trinidad and the Trinidad pitch lake. If one follows the Orinoco River inland from its mouth for some 65 miles, one comes to a village called Guariquen. The so-called Bermudez Lake lies between the edge of a swamp and the foothills near Guariquen in what might be termed a savanna, says Richardson. (20) The “lake”, wrote Richardson, has “an irregular-shaped surface with a width of about a mile and a half form north to south and about a mile east and west. Its area is a little more than 900 acres, and it is covered with sparse vegetation, grass, and shrubs, and occasional groves of large palms, called morichales. One sees no dark expanse of pitch on approaching it as at the Trinidad pitch lake, and except at certain points where the soft pitch is welling up, nothing of the kind can be found. The level of the surface of the deposit does not vary more than two feet and is largely the same as that of the surrounding swamps. In the rainy season it is mostly flooded and at all times very wet, so that any excavation will fill up with water. These conditions make it difficult to get about upon it and to excavate pitch.” (20) 
Map showing Orinoco River with delta opposite Trinidad Island. Source:
http://www.spikehampson.com/images/orinoco_negro.jpg; accessed December 10, 2007. 
Bermudez pitch lake, Venezuela, photographed by Clifford Richardson. Source: Clifford Richardson: Trinidad and Bermudez Lake Asphalts and Their Use in Highway Construction. The Barber Asphalt Paving Company, October 16, 1917, p. 18.
Richardson continues: “It is readily seen that this deposit is a very different one from the pitch lake of Trinidad. It seems to be, in fact, an over-flow of soft pitch from several springs, over this large expanse of savanna, and one which has not the depth of that at Trinidad. At different points there is a depth of 7 feet of material, while the deepest part of the deposit is only 9 feet and the average of pitch below the soil and coke only 4 feet.” The “consistency of the soft pitch at the center of the Bermudez lake is thinner than that of the Trinidad lake. It does not evolve gas in the same rapid way or harden as quickly after collection. It, therefore, does not retain the gas which is generated in it, nor does the deposit as a whole do so at the same extent as the Trinidad pitch.” (21) Richardson concluded that “the Bermudez deposit owes its existence to the exudation of a large quantity of soft maltha [soft mineral pitch], which is still going on and which has spread over a great area; that this has hardened spontaneously in the sun, and has also, by the action of the fires, been converted over almost the entire surface into a crust of some depth, beneath which the best material lies, and that here and there are scattered masses of glance pitch produced in a similar way form the less violent action of heat”. The amount of water the Bermudez asphalt contains varies between 11 and 46%. Bermudez asphalt is completely different in composition from that found in the Trinidad pitch lake, by the absence of emulsified water and mineral matter. It is a purer and softer bitumen and quite devoid of the colloidal clay found in Trinidad asphalt.” (21) Richardson attributed the presence of colloidal clay in Trinidad asphalt, and to the large amounts of sulphur derivatives in Trinidad petroleum and asphalt and Bermudez asphalt, to the desirability of these bitumens in highway construction. (22) X. La Brea “Tar” Pits, Los Angeles, California The famed La Brea “Tar Pits” of Los Angeles today bear little resemblance to their former astonishing selves. Mined for asphalt and then for fossils for a century and then converted into a tourist education spot, their native nature emerges only in descriptions by 18th, 19th and early 20th century observers. The early descriptions suggest a geomorphology strikingly similar to Venezuela’s Bermudez “swamp” of asphalt “springs” described by Clifford Richardson (see above). The distinctiveness of the La Brea “Tar Pits” of Los Angeles, as compared with their Bermudez and Trinidad counterparts in South America, lay in the mind-boggling numbers of extinct mostly carnivorous fossils within the asphalt beds. What did the area look like in its untouched state? 
Map of La Brea Tar Pits (Los Angeles), by Joe LeMonnier. Source:
http://www.naturalhistorymag.com/0607/images/0607feature_LaBreaMap.jpg; accessed December 10, 2007. 
Rancho La Brea pitch lake (Los Angeles, California) as seen by paleontologist John C. Merriam. Source: John C. Merriam: “The fauna of Rancho La Brea, Part I: Occurrence”, University of California, 1911. Available online a
http://www.archive.org/details/faunaofrancholab00merrrich; accessed December 10, 2007. John C. Merriam (1869-1945), a University of California paleontologist, described in 1911 the Rancho La Brea “tar pits”. (23) “The earliest description of bituminous deposits in the Los Angeles region known to the writer,” Merriam wrote, “is found in the narrative of the Portola Expedition written in 1769. ” Caspar de Portola wrote, “The 3rd [August 3, 1769], we proceeded for three hours on a good road; to the right of it were extensive swamps of bitumen which is called cliapapote. We debated whether this substance, which flows melted from underneath the earth, could occasion so many earthquakes.” (23) In 1853, the first geologist to examine the Rancho La Brea asphalt springs was William Phipps Blake (1826-1910), the official government geologist and mineralogist for the Pacific Railroad Survey in the Far West. (24) He wrote: “There are several places in the vicinity of the city (Los Angeles) where bituminous or mineral pitch rises from the ground in large quantities. These places are known as tar springs, or pitch springs, and some of them form large ponds or lakes. One of the springs was passed on our way to the city, and was near the outcrop of bituminous shale in the banks of the creek already described. This spring was nothing more than an overflow of the bitumen from a small aperture in the ground around which it had spread on all sides, so that it covered a circular space about 30 feet in diameter. The accumulated bitumen had hardened by exposure and its outer portions were mingled with sand, so that it was not easy to determine its precise limits. It formed a smooth hard surface like pavement, but toward the center it was quite soft and semifluid, like melted pitch. The central portion of the overflow was higher than its margin, and it was evident that all the hard portion had risen in a fluid state and by the heat of the sun had been gradually spread out over the surface; at the same time being constantly exposed to dust, it had become so thoroughly incorporated with it that the compound had all the consistent of an artificial mixture. ” (23) In 1865, Josiah Dwight Whitney (1819-1896), California’s state geologist, briefly described the asphalt exposures and “tar” pools. (25) Merriam notes, “He [Whitney] referred in his report to the very large amount of the hardened asphaltum mixed with sand and the bones of cattle and birds which have become entangled in it,” but did not state that the remains were those of extinct forms. Whitney wrote: “About seven miles due west of Los Angeles is the most important of the numerous tar-springs seen in this vicinity. It is from here that most of the asphaltum used in the town is obtained. Over a space of fifteen or twenty acres, the bituminous material (which when seen by us, in the winter, had exactly the consistency and color of tar) was oozing out of the ground at numerous points. It hardens on exposure to the air, and becomes mixed with sand and dust blown into it, and is then known as ‘brea’. The holes through which the bitumen comes to the surface are not large, few being more than three or four inches in diameter. On removing the tarry substance from the holes, by repeatedly inserting a stick, the empty cavity was very slowly filled up again. At one place there was a pit several yards square, and six or eight feet deep, from which the tar had been taken; but it was filled with water, at the time of our visit, in consequence of late heavy rains….A very large amount of the hardened asphaltum, mixed with sand and the bones of cattle and birds which have become entangle in it, lies scattered over the plain.” (23) In 1875, Professor William Denton of the Boston Society of Natural History identified the bones at Rancho La Brea as fossils. (25) He wrote: “The locality is known as Major Hancock’s Brea Ranch, and is about eight miles west of Los Angeles, in the valley of the Santa Anna. The bed of asphaltum here covers sixty to eighty acres, and at a depth of thirty feet no bottom has been reached. Thousands of tons have been removed for roofing, paving and combustion, but the supply is almost inexhaustible. Major Hancock had about twenty-five Chinamen employed in digging out the best of the asphaltum, which is soft enough to agglutinate in the heat of the sun. The material conveyed to large, open iron boilers, in which it was boiled for twenty-four hours, and then run into sand molds; subsequently it was broken up, for it is quite brittle after being thus boiled, carted for nine miles and shipped to San Francisco, where it was sold for twenty dollars a ton for making asphalt pavement. The bed is about three miles south of the Santa Monica ranges of mountains, and it appears to lie parallel with them.” “Beds of petroleum shale of tertiary age, having in many places a thickness of about two thousand feet, are to be found along the California coast, and at some distance in the interior; they are said, By Professor Whitney, to extend from Cape Mendocino to Los Angeles, a distance of about four hundred and fifty miles. They are exposed in cliffs on the coast near Santa Barbara and Carpinteria, and other places. This shale, there is good reason to believe, is the deposit from which all the asphaltum of California has been derived.“Although this shale is not exposed in the vicinity of the Brea Ranch, it is exposed in various localities at but a short distance, and doubtless underlies the asphaltum deposit, for hundreds of ‘tar-springs’ exist in the vicinity, from which the material is still flowing over the surrounding locality, the springs being in some cases elevated, by its deposition around them, several feet above the surrounding level. “Major Hancock presented me with what I found to be a canine of a Machairodus, a great saber-toothed feline. It was found at the depth of fifteen feet in the asphaltum. The tooth is nine and a half inches in length…” (23) Denton then describes the tooth at length. John C. Merriam was the next person to recognize the importance of the saber-tooth cat’s canine tooth and the glut of other fossils associated with the Rancho La Brea asphaltum deposits. Merriam initiated the excavation of the site, which continues to this day. 
“Early excavations at the La Brea tar pits of central Los Angeles during the period 1913–1915 unearthed roughly a million bones from nearly a hundred sites.
Photo courtesy of the George C. Page Museum. Source:
http://www.naturalhistorymag.com/0607/images/0607feature_earlyexcavators.jpg; accessed December 10, 2007. 
“All the fossils from the early excavations were housed in the old ‘bone room’ at the Natural History Museum of Los Angeles County, before being transferred to the George C. Page Museum in 1977. Photo courtesy of the George C. Page Museum. Source:
http://www.naturalhistorymag.com/0607/images/0607feature_earlyexcavators.jpg; accessed December 10, 2007. Merriam also described in fine detail the “type locality” of Rancho La Brea: “The formation in which the fossil bones occur at Rancho La Brea is essentially an alluvial accumulation consisting mainly of beds of clay, sand, and asphalt. In some places bedding planes are quite distinctly shown, especially in the clay or sand strata. At other localities the deposit has been irregular in pockets, and minor local movements of the asphalt or clay masses has possibly increased the irregularity of the beds. The asphalt may occur as a nearly pure bituminous deposit, though it is usually mixed with sand, clay, or other materials. In some places it appears as fairly definite strata, while at other points it has irregularly impregnated beds of sandy or clayey material, and no definite bedding is shown. “The thickness of the asphalt deposits containing bones has not been determined, but these beds probably extend considerably deeper than the lowest levels yet reached. A depth of at least thirty feet is recorded for the work carried on by Major Hancock, and nearly the same horizon has been attained in recent excavations. “The formation in which the asphalt appears has been penetrated by the wells in the Salt Lake Oil Field immediately to the north of the principal brea outcroppings, and seems also to be a part of a series of beds comprising a considerable thickness of sand and clay strata exposed in the hills immediately to the south. The well records of the Salt Lake Field, as described by Arnold, indicate the presence of Pleistocene strata from fifty to one hundred feet in thickness overlying the Tertiary formations in which the main oil-bearing beds are found. The Pleistocene section penetrated by the oil wells comprises alluvium, clay, coarse sand, gravel, and asphalt, the deposits being apparently all of fresh-water or alluvial origin. Asphalt is well represented down to the bottom of the Pleistocene portion of the section. 
Cross-section sketch of Rancho La Brea Tar Pits. Source:
http://www.tarpits.org/education/guide/geology/asphalt.html; accessed December 10, 2007. 
Cross-section sketch of Rancho La Brea Tar Pits. Source:
http://www.tarpits.org/education/guide/geology/asphalt.html; accessed December 10, 2007. “The formation exposed in the low, flat ridges immediately to the south of Rancho La Brea is apparently a part of the series represented by the fossil-bearing strata at Rancho La Brea and by the Pleistocene penetrated in the oil wells of the Salt Lake Field. The ridges south of the fossil beds are considerably eroded and terraced, and it is to be presumed that the erosion which is indicated occurred in Pleistocene time. It is therefore probable that the fossiliferous beds now exposed at Rancho La Brea were at one time covered by many feet of strata, which have been removed by erosion inaugurated before the beginning of the Recent epoch…” (23) Today the La Brea Tar Pits tourist site, named Hancock Park, offers visitors a sanitized version of the true going-ons of the hot deep geo-biosphere, which lurks beneath the museums, souvenir store, and excavated pits filled with dark liquid and life-size replicas of thrashing extinct animals tethered to stakes at the bottom of the pit. On Sunday, March 24, 1985, for example, methane, associated with pitch lakes, surreptitiously collected in the basement of the Ross Dress-for-Less store near the La Brea Tar Pits and exploded, sending two dozen people to the hospital, some critically burned. (27) Writer William L. Fox lives near the La Brea Tar Pits and often meditates on methane bubbles breaking the surface of the ponds as other passerbys flick their cigarette butts onto the bubbles in hopes of igniting them. Fox says laconically, “Los Angeles lies in an active seismic zone atop an oil field.” (27) XI. Summary “Pitch lakes” (natural asphalt deposits) in Trinidad, Venezuela, and Los Angeles are the surface manifestations of active geologic and biologic processes in the deep hot earth, about which very little is known. Sources:
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