Reddit reviews Trees of Central Texas: A Guide to Common Native Species (Quick Reference Guides)

I use the TX A&M Forestry Service oftentimes in the field, works ok from a smartphone. We also carry a copy of this guy in the glove box of the truck. There is a pretty decent introduction on there, as well, that kinda outlines the basics of tree ID'ing. The tough thing about starting right now in our neck of the woods is the time of year, most trees around here are barren of leaves so you have to go off dead leaves on the ground, branch patterns, and bark.

Good luck! It sounds like a tough endeavor, but tree surveys are fun times, man.