The Imperial Valley of Southern California lies in Imperial and Riverside counties, with an urban area centered on the city of El Centro. The Valley is bordered by the Colorado River to the east and, in part, the Salton Sea to the west. Farther west lies the San Diego and Imperial County border. To the north is the Coachella Valley region of Riverside County, whic…The Imperial Valley of Southern California lies in Imperial and Riverside counties, with an urban area centered on the city of El Centro. The Valley is bordered by the Colorado River to the east and, in part, the Salton Sea to the west. Farther west lies the San Diego and Imperial County border. To the north is the Coachella Valley region of Riverside County, which together with Imperial Valley form the Salton Trough, or the Cahuilla Basin, also the county line of Imperial and Riverside counties, and to the south the international boundary with Mexico.