Geology of Tecolote Tunnel: ABSTRACT

Abstract

The Tecolote Tunnel, one of the essential features of the Bureau of Reclamation's Cachuma Project, is located in the southeast part of Santa Barbara County, California. The tunnel, now under construction through the Santa Ynez Mountains, connects Cachuma Reservoir in the Santa Ynez Valley with the narrow coastal plain in the Santa Barbara region. Rocks penetrated have a stratigraphic thickness of more than 10,000 feet, range from upper Miocene to middle Eocene age, and include the following formations: Monterey, Rincon, Vaqueros, Sespe, Alegria, Coldwater (Sacate), Cozy Dell, Matilija, Anita (Juncal), and possibly Jalama (Upper Cretaceous age). Three major structural units are found along the tunnel line: (1) the south limb of a major east-west-trending anticline, cut off on the north side by the Santa Ynez fault; (2) a much broken, moderately sheared and deformed, homoclinal sequence which is bounded on the south by the Santa Ynez fault and on the north by a minor fault zone; and (3) a minor northwest plunging syncline. Regularly spaced samples of rock in the tunnel have been and are being taken for the purpose of lithologic, paleontologic, and porosity-permeability studies. Preliminary work on the microfossils from these samples reveals a prolific Miocene fauna but a rather sparse yield from the Eocene. Parts of the tunnel have been logged by using conventional radioactivity (gamma ray) logging equipment with lead shields spaced normal to the ionization chamber. Favorable correlations are found between the log and lithologic units. Uncemented sands, washed and blown into the tunnel by formational water and gas, have caused much delay in progressing through the Santa Ynez fault zone. Large flows of water, more than 4 million gallons per day, from fractured parts of the Cozy Dell formation have also impeded progress. Very minor traces of petroleum have been observed in both of these sections of the tunnel. End_of_Article - Last_Page 2634------------