GEOLOGY OF THE SAN DIEGO & ARIZONA EASTERN RAILWAY, SAN DIEGO AND IMPERIAL COUNTIES, CALIFORNIA, U.S.A. AND BAJA CALIFORNIA, MEXICO

In 2003 and 2004, a reconnaissance study of geologic, historic, geographic and cultural settings was conducted across the Peninsular Range following the 139 mile-long alignment of the San Diego & Arizona Eastern Railway.The study extended southward from San Diego, California into northern Baja California, Mexico, re-entered the United States near the crest of the Peninsular Range mountains, then descended eastward through the Carrizo Gorge into the Salton Basin of the Colorado Desert.

Mapping of the geology along the railway alignment reveals a cross-section of Paleozoic through Early Cretaceous metamorphic and igneous rocks intruded by Jurassic through Late Cretaceous plutons of the Peninsular Range Batholith. Later Tertiary through Quaternary rocks overlap the edges of the central peninsular massif.

More detailed studies, especially within metasedimentary rocks of the Carrizo Gorge segment, allowed some preliminary assessments of structural geology and potential geotechnical constraints along the reactivated railway. Faults, landslides, rockfalls and potentially adverse slope conditions in weak rocks along the railway and within tunnel openings are approximately delineated.

Particular attention is paid to Tunnel No. 7 for future re-opening and landslide buttressing, Tunnel No. 8 groundwater seepage for drainage and grouting, the unique wooden trestle at Goat Canyon for landslide stabilization and trestle scour-protection, and Tunnel No. 16 for east portal slope-stabilization.

A review of ongoing operations of the railway and recommendations for future improvements indicates fulfillment of a 150 year-old dream of San Diegans for an eastern "main stem" railway that connects this important corner of the United States to a multinational rail network.