Pflugerville sits east of I-35 and east of the escarpment, squarely in the Blackland Prairie. The bedrock is Upper Cretaceous calcareous mudstone, marl and chalk, and the soil above it is deep clayey residuum weathered from that material.
That soil is highly expansive, and it is the dominant design constraint on every slab in the city. The characteristic Houston Black series is very deep, greater than 80 inches, holds 40 to 60 percent clay, and forms slickensides and cracks half an inch to four inches wide that reach at least a foot down and stay open 90 to 150 days a year. Permeability is very slow, so runoff is high.
There is effectively no rock to encounter. Nobody in Pflugerville is paying for a rock breaker.
What makes the city interesting to work in is the age spread. Springbrook, Windermere, Heatherwilde and Swenson Farm went in through the late 1990s and 2000s. Blackhawk, Falcon Pointe, Avalon, Sorento and Carmel are 2000s to 2020s. We see original flatwork at both ends of its life here, which is a useful education in what actually lasts on this soil.