Bulletin - United States Geological Survey Volume 405-406 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 Excerpt: ...R. 20 E., along the summit of the range to Crocker Spring. A similar siliceous stratum, in which the shale is of a porcelaneous type, lies near the top of the Monterey. It appears to be a silicified diatomaceous shale. The steep southwest wall of Salt Creek canyon exposes a fine section of the Monterey, which is there a southwest clipping monocline of platy, limy, siliceous yellow shale, containing hard yellow7, limy concretions which are seamed with numerous small calcite veins. After long exposure to the weather, the less resistant portion of the. concretions is dissolved away and the harder veinlets left in bas-relief. This sort of weathering is typical throughout the whole series, wherever there is differential hardness in the calcareous portions of the shales. Of such character are the shales a couple of miles west, and as far south, of Frazer Spring. This phase of the shale occurs also at the south end of Santa Maria Valley in the broad flat-topped ridge lying mostly within sec. 6, T. 31 S., R. 22 E. The topography of the uppermost beds of the Monterey southwest of Midway contrast rather sharply with the lower smooth slopes of the softer shales of the Santa Margarita(?) formation. The former is clayey and carries more numerous and more thinly bedded brownishellow calcareous concretions than exist higher in the series. The steeply northeastward dipping shales at Crocker Spring are probably in this upper zone of the Monterey. In all the folded upland region along the summit of the Temblor Range there is little lithologic variation in the Monterey shale except that due to folding or faulting. The intergradationary character of the Monterey and Santa Margarita(?) and their close resemblance is, nevertheless, very evident along this zone; beds of coarse gr...