Wednesday, March 13, 2013



One of the major subdivisions of the northern Colorado Plateaus is the Uinta Basin, a large basin associated with the Sevier/Laramide (Cretaceous & early Tertiary) Orogeny and located in eastern Utah south of the Uinta Mountains.  The Basin is a structural basin, as opposed to a topographic basin, meaning that it is a very large syncline, and a compliment to the anticlinal Uinta Mountains.  The structure is related to the Piceance Basin of northwestern Colorado, and the Fossil and Green River Basins north of the Mountains in Wyoming.  The rocks in the Basin are an interesting sequence of latest Paleocene (~58 my) to early Oligocene (~28my) basin-fill sediments consisting of, in ascending order, the Colton Formation (stream and flood plain deposits), the Green River Formation (Lake Uinta, part of a large fresh water lake system), the Uinta Formation (lake edge and lake filling sediments), and the Duchesne River Formation (stream and flood plain sediments on top of the lake sediments.

The Basin is well-known for its production of oil and gas, as well as for interesting examples of solid hydrocarbons--kerogen-rich mudstone (oil shale) and bitumen-impregnated sandstone (tar sands).  But perhaps the most interesting hydrocarbon in the Basin is one that a few years ago (pre-1995) would not be classified as a ”mineral” and that is Uintaite, referred to in this article as the trade name Gilsonite.  In 1995 the International Mineralogical Association adopted a new definition of a mineral as “an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes” (Nickel, 1995).  This definition opened the way for an organic class of substances that included hydrocarbons of which Gilsonite is a member.  Gilsonite is a solid hydrocarbon that comes from the solidification of petroleum.  It is usually a dull black in the field and resembles coal; however, some fresh surfaces are quite shiny with a conchoidal fracture and superficially looks a little like obsidian.
Gilsonite in the Uinta Basin occurs in long veins (measured in miles) from a few inches to several feet thick and hundreds of feet in a vertical direction.  Most thick veins occur in the Green River and Uinta Formations, both units are Eocene in age.  In fact, the veins seem “rooted” in the oil shales of the Green River Formation.  Tripp (2004) believes the Gilsonite had its beginning in the large amounts of organic debris that accumulated in the sediments of tropical Lake Uinta.  The burial of these sediments created heat and pressure and the Green River oil shales were formed.  Again, burial of the oil shales created water and hydrogen and this explosive mixture was expelled and created fractures in the surrounding rock.  These fractures were later filled with petroleum whose viscosity disappeared with desiccation.  Gilsonite is essentially solid “oil”.
Gilsonite was “discovered” by Caucasian settlers in the 1860’s although most did not know of a good use for the substance as it melted and ran from the stoves when used as a substitute for coal.  In the 1880’s a Mr. Samuel Gilson begin to market (as St. Louis Gilsonite Company) “asphaltum” as a waterproof substance and as an electrical insulator.  However, two major problems arose: 1) many of the thick veins of Gilsonite were on the Uintah-Ouray Indian Reservations; and 2) a railroad did not extend into the Uinta Basin and Vernal (and even today the Basin is without rail transportation).  Gilsonite and Uinta Basin boosters took care of the first problem as the U. S. Congress simply took away 7000 acres from the Native Americans (Burton, 1996)!  By around 1900 the Gilson Asphaltum Company (now called the American Gilsonite Company) was the major player in Gilsonite and had consolidated several claims; however, “trucking” (used freely since horsing may be a better term as horse-drawn wagons were used) the Gilsonite 80-100 miles to a Utah rail head was not a very viable option.  So, as with so many projects, “necessity is the mother of invention” (att. To T. Veblen).  The necessity was transportation and the “invention” was the Uintah Railway--started in 1903 and completed in 1911.  The Uinta Basin terminal was at Rainbow near the mines while the southern terminal was at Mack, 22 miles west of Grand Junction, CO, on the Rio Grande Western Railway.  In between those two points was a three foot wide track (narrow gauge) traversing Baxter Pass (8473 feet) and approximately 63 miles of crookedness, curves and grade. The first 28 miles, coming from the south, had 36 bridges while at some of the steepest grades the brakeman could walk faster than the train.  On a few curves the engineer could shake hands with people in the caboose, or so it was said (The Uintah Railway, no date).

The Uintah also hauled passengers, freight, mail and livestock but was abandoned in 1939.  Perhaps its best known cargo---the Dinosaur bones Earl Douglas quarried from what is now Dinosaur National Monument but were then shipped to the Carnegie Museum in Pittsburg.  Today a few grades remain and I have done some hiking along the railway route.  In the 1970’s spikes associated with the tracks were common; today, rare. 

After abandonment of the railway, Gilsonite was shipped by truck from a new processing plant near Bonanza, UT.  In the 1950’s a slurry pipeline was built from Bonanza to near Mack, CO, and gasoline was distilled from the mineral until the 1970’s.  Today, American Gilsonite Company continues to mine away in the Basin and sells its product for use in “160 products, primarily in dark-colored printing inks and paints, oil well drilling muds and cements, asphalt modifiers, foundry sands additives and a wide variety of chemical products” (American Gilsonite Company at  If visitors travel to the Basin on U. S. Highway 40 it is a very worthwhile trip to make the detour to Bonanza and the abandoned mines.  The deposit is unique and the mines and abandoned facilities are “ghost-like”. 

And, for a special treat, check out the video of the railroad at:

Burton, D. K. 1996, A History of Uintah County: Scratching the Surface in Utah Centennial County History Series: Salt Lake City: Utah State Historical Society, Salt Lake City. 

Nickel, E. H., 1995, The Definition of a Mineral: The Canadian Mineralogist, v. 33, no. 3.
The Uintah Railway, 2009:

Tripp, B. T., 2004, Gilsonite, an Unusual Utah Resource: Utah Geological Survey Notes, v. 36, no. 3.