Palo verde means green wood in spanish.  Palo verde trees, in the Cercidium genus, tell you that the soil contains more water than normal dry desert slopes.  Sometimes the roots access soil water collected in bedrock depressions, almost like subterranean tiny ponds. Like mesquite, palo verde also grows close to washes so it can soak up as much water as possible through its deep root system.  Also like mesquite, it can take on either a shrub or tree form. 

When conditions are wet enough, the tree will sprout leaves.  During dry periods, however, the leaves drop.  This adaptation to drought is called drought deciduous behavior. During dry periods, palo verde trees photosynthesize using the chlorophyll in the bark.