High Quality Content by WIKIPEDIA articles! The Pomona Valley, located between the San Gabriel Valley and Cucamonga Valley in Southern California, straddles the border between Los Angeles County and San Bernardino County. Back on March 1, 1893 the California Assembly voted 54-14 for a new county to form in the region, San Antonio County, with Pomona as its seat. Los Angeles interests in the Senate rejected the concept, however, and today the eastern and western portions remain divided between San Bernardino and Los Angeles counties. Physical dividing lines separating the Pomona valley from the San Bernardino Valley on the east include: the San Antonio River, the eastern border of the Watershed of the San Antonio River, and Interstate 15/Etiwanda Avenue. The Pomona Valley is separated from the San Gabriel Valley to the west by the San Jose Hills running approximately along State Route 57. The valley lies south of the San Gabriel Mountains and north of the Chino Hills. The historic Route 66 runs through the Pomona Valley.