Texas Hill Country History

From time to time, I reckon I'll post some geologic histories that ring with poetry and vision.  I've read lost - McPhee of course is a given - but this is the first I've come across since moving to Mt. Lucas.  Enjoy.

From  Texas Hill Country by George Oxford Miller, 1991

The rugged hills in the heart of Texas was born of fire and water, the basic elements that Aristotle used to represent continual conflict.  Like a detective, a trained observer can decipher the ageless turmoil in the twisted, melted and worn rock strata.  A casual traveler cannot help but see and feel, and perhaps marvel at, the results of the eternal conflict.  You see the first evidence of it just west of IH 35 between Georgetown and San Antonio.  A low range of hills juts out of the blackland prairie.  The deep scars from rock quarry strop mines recall that Texas has a heart of stone – limestone.

This juncture of flat prairie and rugged limestone hills results from one of the most important geological features in Texas, the Balcones Fault.  The upper side of the fault stretches like a spread-out horseshow from Del Rio to San Antonio and curves north through Austin.  It disappears underground near Temple.  Within the open semicircle of the fault line, nature’s cycle of deposition and erosion has sculpted the Edwards Plateau into the rugged Hill Country.  At the edge of the fault, hills rise out of the prairie sod and great springs gush crystal-pure water at the rate of millions of gallons per day.  Humans have lived near the springs at Del Rio, San Antonio, New Braunfels, San Marcos and Austin for thirty thousand years. 

Few of us stop to contemplate that events that transpired millions of years ago dictate our profession, recreation and culture.  But by supplying water, soil and minerals, the lay of the land directs the society it sustains.  The essence of the Hill Country as we know it today – its resources, its character, its charm – is inherited from its geological past, the series of events that began sometime back in geological time (that means so long ago that it boggles our minds) and stretches through today and into the unforeseen future.

As you climb west onto the Edwards Plateau, say on Texas 71 or US 290, you are traveling backward through geological time.  You can time-travel back 135 million years and find dinosaur tracks in the flat rock bottoms of the Blanco and San Gabriel rivers.  Step back 300 million years at Pedernales Falls State Park and discover crinoids in the rock strata along the river.  But don’t stop yet.  At the San Saba River bridge south of Brady, you can journey back 600 million years and see fossils of some of the earliest known life forms, sea algae resembling two-foot lily pads.  The road into the past continues beyond the emergence of life to a time when the earth was in its infancy.  The Valley Spring Gneiss  at Inks Lake State Park dates back one billion years.  The pinkish crystals of feldspar were formed deep within the earth in rocks subjected to intense heat and pressure, and exposed to modern eyes by uplift and erosion.

So the roots of the Hill Country date back to primordial time when the continents were just forming.  Since then, nature’s cycle of deposition and erosion has shaped and reshaped this area countless times.  Curing the Cambrian era, 5 to 6 million years ago, shallow seas covered central Texas and deposited thick sediments of limestone, shale and marine sandstone.  Then the seas receded and erosion began wearing away the solidified sediments.  The cycle was repeated about 450 millions years ago and Ordovician seas laid down 1,400 feet of limestone known today as the Ellenburger group.  Geologists find shallow sea deposits from 350 million, 300 million and 85 million years ago.  During the late Cretaceous period, about 75 million years ago, a great uplift began pushing the coastline hundreds of miles to the east and exposing an eastward-sloping plateau of sedimentary rock thousands of feet thick.  Just as life itself once had, the Edwards Plateau emerged from the sea.  In moist periods, such as the ice ages, rivers ran deep and wide and cut steep valleys.  During the brief interval of geological time since the plateau’s emergence, rain and wind have sculpted the hills we see today. A look at the level horizon reveals that this rugged terrain was carved from a flat slab of limestone.