Mesquite - this small tree is ubiquitous here. It is an extremely hardy and drought-tolerant plant. It grows fast, and it's a refuge for wildlife where other trees won't grow. It is a legume which means it fixes nitrogen in the soil. This improves soil fertility. Bees are attracted to the flowers and mesquite honey is prized. I probably have 30 trees on the Double Barrel Ranch.
Acacia- another small tree that is also common but has a more pleasing shape than a Mesquite. It also is low water use. But it is often liberally protected by thorns. This explains some of the common names such as "catclaw" or "wait-a-minute tree." The flowers are very fragrant though. I have about a dozen Acacia of a couple different varieties.