From Alamo Lake, the (short) Bill Williams River flows due west for 35 mi to meet the Colorado River. The Bill Williams River is the de facto border between the Mojave Desert north and northwest; the Sonoran Desert is south and southeast. Across the south-flowing Colorado River to the west, is the massif of the Whipple Mountains at the northeast of the Sonoran Desert subsection named the Colorado Desert of southern California and bordered by the Colorado River.