Creosote bush is the most common perennial shrub on Tempe Butte, growing about 1 to 2 meters tall.  These very hardy plants are able to thrive in very dry places away from washes.  Some researchers think that these plants migrated to the Sonoran Desert about 10,000 years ago, and really expanded its range in the last 6000 years to become the most common shrub in the Mojave and Sonoran Deserts.