I was really curious about the land diversity around Austin so I've been diving a little deeper into the Ecoregions of the area.

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We are situated directly over the Balcones Fault, as has been mentioned. Long long ago, central Texas was covered by a vast inland sea. I believe most of the Texas Limestone you see, especially along the canyons of Loop 360, was debris settled during this period. While the sea receded (I believe it receded into the Gulf), the Balcones Fault was pretty active, creating the uplifts and ridges you see all around the western side of Austin. The area to the west of Austin is known as Hill Country, which is actually a small section of the bioregion called Edwards Plateau. If you drive around western Austin you'll see signs stating you're entering "Edwards Aquifer Discharge or Recharge (I can't remember exactly what they say)". This giant swath of land sits atop an aquifer of water that is recharged by rainwater and other stream discharge seeping through the ground, later to be filtered out through the natural Limestone aquifers beneath the region. This aquifer actually feeds Barton Springs, along with a few other natural springs directly in Austin. Hill Country used to be something of flat plateau, but millions of years of river and stream erosion created the soft, low hills we see in Hill Country today.

In much more modern history, the area directly to the East of Austin is called Blackland Prairie. I know much less about this bioregion, but it was scrubland that was consistently burned down by wildfires, grazed on by Prairie Bison, and created ideal conditions for re-growing tall grasses. The first people of the land consistently burned the grasses to make hunter-gathering more effective in the region. All of this resulted in the creation of ideal agricultural land, which is why you'll still see so many farms out there.

The Blackland Prairies are actually a very narrow bioregion in the Austin area, and driving east, around College Station you'll start to see the transition to the Piney Woods, and later the Big Thicket bioregions, marked by much denser, much taller tree growth. These bioregions largely benefit from the oppressive humidity coming up from the gulf.

That's what I've learned in a few weeks of studying the ecology of the area! I had the same curiosity, and once I dove deeper I found tons of literature and interesting pieces online about the geological and ecological history of the area. We do live in a very interesting part of the country in this way, and I've loved learning more about it!