Alta Loma is one of three formerly unincorporated areas that became part of the city of Rancho Cucamonga, California,United States in 1977. The community is located at in the foothills of the south face of the San Gabriel Mountain range, near Cucamonga Peak and Mount San Antonio (Mount Baldy). Its zip codes are 91701 and 91737. Elevation ranges from 1,400 feet (430 m) to 3,000 feet (910 m). The name comes from the Spanish words for "high hill." Alta Loma had previously been known as "Iamosa".
Rancho Cucamonga, Alta Loma and Etiwanda were most affected by the October 2003 Grand Prix fire, which combined with the Old Fire. The Grand Prix fire, which began October 21, 2003, ripped across the mountains just above and, in some places, down into Alta Loma and Etiwanda for six days. Overgrown brush fueled fire, which ran across the mountain tops and higher foothills to eventually fly into the canyons that are surrounded by homes. It destroyed 13 homes (including 2 mobile homes) and five outbuildings, and damaged 9 others in Alta Loma.