I’ve been searching to understand why the Palo Pinto Mountains stretch southeast to northwest, and why the Brazos flows through them at a cross section, northeast to southwest.
TOPOGRAPHY. The region is one of considerable relief, some of the hills rising to heights of 500 feet above the valley floors. The ruggedness of the surface is produced by a series of escarpments which trend in a northeasterly direction and are formed by the outcropping edges of sandstone and limestone beds that dip at low angles to the northwest. The most prominent of these escarpments, about 200 feet above the adjacent plain, is that formed by the group of limestone beds which caps Kyle Mountain. Northwest of this escarpment the country is very rough and in part is heavily timbered. East of the escarpment is a belt of comparatively open country about 5 miles in width, the surface of which, formed by a limestone bed lower than 54 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1915, PART II. that which caps Kyle Mountain, is covered only by a growth of mesquite. The eroded edge of this lower limestone bed forms the crest of another escarpment, southeast of which are a series of timbercovered escarpments formed by sandstone strata. The county is crossed from northwest to southeast by Brazos Eiver, which flows in wide intrenched meanders, suggesting that its course was chosen when it flowed on a low-lying and featureless plain, which has since been uplifted and eroded. The present stream valley is comparatively narrow and is bordered by high bluffs. https://pubs.usgs.gov/bul/0621e/report.pdf
After at least an hour of more searching, I finally found a name for these escarpments: Mineral Wells-Newark East Fault System.
Wikipedia has this to say about it: “Major structural features include the Muenster and Red River Arches to the north, and the Bend and Lampasas Arches along the central part of Province 045. Along the east portion is an area that includes the Eastern Shelf and Concho Arch, collectively known as the Concho Platform. The Mineral Wells fault runs northeast-southwest through Palo Pinto, Parker, Wise, Denton Counties and joins with the Newark East fault system. The fault system bisects the Newark East Field (NE-F) creating a zone of poor production in Barnett Shale gas reservoirs. Several faults that cut basement and lower Paleozoic rocks in the southern part of the province are identified at the Ordovician Ellenburger Group stratigraphic level. These faults and associated structures formed during development of the Llano Uplift and Fort Worth Basin with faulting ending by the early Missourian.
I’d been wondering if the Llano Uplift that produced the famous Texas Hillcountry and the very ancient Oachita Mountain chain that went from Big Bend to Arkansas had anything to do with it. They are why the rivers flow the general direction they do, and the Fault is what the Brazos crosses through northwest of me. All this specific information comes from oil field research, not geology college sites which focus on general ages and more famous landmarks like the Rockies and Big Bend. This sad profit motivated research reminds me of how many techno-advances come during wartime.