Geological Map of Texas

University of Texas, Bureau of Economic Geology
Austin, 1919

E.L. Porch, Jr., Geological Map of Texas, Austin: University of Texas, Bureau of Economic Geology, 1919, Map #94091, Map Collection, Archives and Records Program, Texas General Land Office, Austin, TX.

The University of Texas at Austin established the Bureau of Economic Geology and Technology, the institution’s oldest research unit, in 1909. It serves as the State Geological Survey of Texas to “inform the state’s policy-makers on issues arising from the geology and physical environment of Texas.”[1] To support this mission, in 1919 the Bureau published this map providing both a wide view of the bands of geological formations spanning Texas as well as detailed topographical and subsurface data, which together illustrate the state’s physiographic diversity.

[left] A note on the map lists the sources researchers used in its compilation. [right] In Central Texas, Llano is the site of diverse geological formations including Intrusive Igneous (red), Pre-Cambrian (brown), Cambrian-Ordovician (orange), Comanchean Cretaceous (green), Pennsylvanian (gray with horizontal lines), Paleozoic Undivided (solid dark gray), and Permian (solid light gray).

Using original research to create “essentially a compilation of earlier publications on the geology of Texas,” researchers collected information from dozens of maps. Sources included rare manuscripts from the U.S. Geological Survey, the U.S. Post Office Department, the Louisiana State Geological Survey, the U.S. Coast and Geodetic Survey, the U.S. General Land Office, the Texas Railroad Commission, and the Texas General Land Office.[2] The science of geology was vital at a time when “concepts of the origin, migration, and accumulation of oil and gas advanced rapidly from 1918 to 1926,” making the knowledge gathered on this map critical to Texas’ emerging oil and gas industry.[3]

A legend illustrates the state’s geological formations.

In the lower-left corner, a legend includes seventeen color-coded formations, defined by the U.S. Geological Survey as “the fundamental unit in the local classification of rocks into geologic units based on similar characteristics in…color, mineralogic composition, and grain size.”[4] The map names and identifies each unique formation in detail, including the types of rocks and minerals and their locations. The Bureau superimposed these formations over a standard map of the state that includes counties, county seats, waterways, and railroads to provide an immediate visual understanding of the different geological regions of the state.

[left] The map includes vertical cross-sections for four regions at a scale of 2,000 feet per inch. [right] A detailed view of the Northern Trans-Pecos region.

Four vertical sections in the map’s upper-left corner provide detailed information on subsurface strata at a scale of two thousand feet per inch for locations in the Southern Trans-Pecos, Northern Trans-Pecos, Central and Gulf Coastal Plain, and Llano Estacado and Spur Well regions. At the bottom of the sheet, four horizontal cross-sections detail specific portions of the map labeled with letters A through D, the largest of which stretches from Deaf Smith County in the Panhandle to Galveston on the Gulf Coast.

[top] Four lines show regional elevations and subsurface formations, the longest stretching from the Panhandle to the Gulf Coast. [bottom] A detailed view of the line stretching from San Angelo to Austin.

The area including the East Texas Oilfield, discovered in 1930, receives no special attention on the map.

Notably, the map pays no special attention to northeastern Texas. A little over a decade after its publication, prospector C.M. “Dad” Joiner discovered the East Texas Oilfield in Gregg, Rusk, Upshur, Smith, and Cherokee counties, an area thought to be devoid of oil resources. This area appears on the map as part of an Eocene formation, which the legend describes as “mainly sands and clays; lignite, oil, gas, brick clays, pottery clays, and artesian waters.” The site was the largest oil deposit in the continental United States, and its discovery forever transformed the state’s energy industry.[5]

1. UT Bureau of Economic Geology, “State Geological Survey,” accessed September 8, 2021, https://www.beg.utexas.edu/outreach/state-geological-survey.
2. UT Bureau of Economic Geology Records, 1874–1988, Center for American History, The University of Texas at Austin.
3. Edgar W. Owen, “Remarks on the History of American Petroleum Geology,” Journal of the Washington Academy of Sciences 49, no. 7 (1959): 256–57.
4. United States Geological Survey, “Definition of Terms,” accessed September 8, 2021, https://pubs.usgs.gov/ha/ha747/pdf/definition.pdf.
5. Julia Cauble Smith, “East Texas Oilfield,” Handbook of Texas Online, accessed September 8, 2021, https://www.tshaonline.org/handbook/entries/east-texas-oilfield. Published by the Texas State Historical Association.