MOUNT BONNELL AS AN URBAN GEOHERITAGE SITE IN AUSTIN, TEXAS

Mount Bonnell comprises a popular city park with a commanding view overlooking Austin and the impounded Colorado River, thereby presenting evidence for geologic controls across a socioeconomic borderland. This location functions as a worthy Geoheritage site for Central Texas. The Bureau of Economic Geology, which functions as the State Geological Survey of Texas, in partnership with the City of Austin, created a Texas GeoSign here in 2021 (https://www.beg.utexas.edu/geosign). The Bureau also produced a YouTube video about Mt. Bonnell and the Balcones Escarpment with the goal of reaching an off-site audience (https://youtu.be/UtARsaoJ99k). Local media featured stories about the sign, broadening the sign’s reach.

Mount Bonnell occupies the upthrown side of the main fault line within the Balcones Fault Zone in Austin. With a displacement of roughly 200 m, long-term erosion has sculpted the Balcones Escarpment, which extends southwest from Austin through San Antonio and on to the Rio Grande near Del Rio. Although the escarpment is a discontinuous topographic break, it marks the boundary between two grand physiographic provinces of North America: the Great Plains to the west and the Gulf Coastal Plain to the east. This break also extends north to include the buried Ouachita orogenic belt that underlies Temple, Waco, and Dallas–Ft. Worth. The Balcones–Ouachita borderland provides resources of great value to the human economy: prime cropland along the inner reaches of the Coastal Plain; prolific springs near the foot of the escarpment; and rangelands on the upfaulted carbonate rocks where hilly terrain is rapidly being transformed by residential and commercial development. This geo-cultural break marks the boundary of the American West in Texas.