There are several sources of information on the soils in Texas. The place to start is the Web Soil Survey, from the USDA-Natural Resources Conservation Service (formerly the Soil Conservation Service). They publish “soil surveys” for each county, in cooperation with state agencies.
You can also find specific information on Texas soils in the Texas Soil Characterization Database, compiled by Texas A&M University’s Soil & Crop Science Department. Maps and analytical information for over 100 soils can be found on the Soil Characterization Laboratory’s web page.
Proposed State Soil of Texas: Houston Black
General Soils Information
Soil Basics – from the Soil Science Society of America
Soil Health – from the USDA-Natural Resources Conservation Service
Earth-Kind® Landscaping – improving landscape soils, from Texas A&M AgriLife Extension