Later, known as Warner Pass, named after Juan Jose Warner the owner of Warner's Ranch, it was the place where the Southern Emigrant Trail, the major southern route into California for Americans from the east in the middle 19th Century, passed over the mountains from the Colorado Desert to the coastal regions of Southern California. This made it important as the major gateway to Southern California until the completion of the Southern Pacific Railroad through San Gorgonio Pass to Yuma, Arizona in the 1870s.