A major defining feature of the basin is the karstic nature of the geology. With the porosity of such geology, as well as the numerous tributaries and extensive groundwater supplies, the springs and seeps (PDF) of the Blanco River Basin are home to numerous rare species of invertebrates.
A defining feature of the basin is the karstic nature of the geology. The area is characterized by shallow extensive limestone bedrock and a lack of deep top soils, making it particularly vulnerable to scouring from increased water velocities. Rain events are converted to major pulses of overland flow to the river. Dry uplands are dominated by sloped, mesic canyons which support smaller trees on their shallow soils. Relatively little water is retained in surface layers due a paucity of top soils and degraded vegetative cover.
Rainwater infiltrates or percolates quickly through extremely porous limestone into water-bearing layers of aquifers. As the Blanco River encounters many fractures or faults along its course, water disappears underground and reappears downstream in multiple locations along its course.