Eastern Transportation Corridor (State Route 241), and the two-lane Ortega Highway (State Route 74) connect the regions. Highway 91, which follows the Santa Ana River through a pass between the Santa Ana Mountains on the south and the Chino Hills on the north, is one of California's most congested routes. Because of this, several proposals have been floated to excavate a highway tunnel through the Santa Ana Mountains, although the multibillion-dollar idea has drawn criticism from environmentalists and others concerned about cost and safety in the earthquake-prone region. While Highway 91 is one of the most congested routes in California, Highway 74 holds a more ominous claim as one of the most dangerous highways in the state. State route 241 starts in Mission Viejo and travels along side the Foothills of the Santa Ana's while merging with State Route 133 and 261. The highway finishes at the junction with State Route 91. References Notes External links Archival collections Guide to Geology of the South Flank of the Santa Ana Mountains, by Paul H. Dudley. Special Collections and Archives, The UC Irvine Libraries, Irvine, California. Other The Nature Conservancy: Santa Ana Mountains Santa Ana Mountains Wild Heritage Project Naturalist For You Cleveland National Forest Center For Biological Diversity Santa Ana Mountains Natural History Association Santa Ana Mountains wildlife Peninsular Ranges Mountain ranges of Orange County, California Mountain ranges of Riverside County, California Mountain ranges of San Diego County, California Cleveland National Forest Geology of Riverside County, California