Precipitation decreases westward until west coast a. Annual precipitation totals small. B. Other influences on vegetation 1. In addition to rainshadow effects, creates elevation zones that mimic latitude. Region generally not glaciated, expect in mountains.
Fires become more common.
Decreasing precipitation, longer periods of soil water deficit and drought. Precipitation increasingly concentrated in summer season. Too dry for forests. Massive woody tissue cannot be maintained during extended deficits. Present only where permanent groundwater supply approaches surface.