Santa Cruz County History - Making a Living

Mineral Survey of Santa Cruz County - Bituminous Rock
by C. McK. Laizure

Prepared by C. McK. Laizure,
Mining Engineer of the California State Mining Bureau

The deposits of asphaltic and bituminous rock in Santa Cruz County have long been known and utilized. The material is a porous, loose, fine to fairly coarse-grained sandstone, impregnated with asphaltum. These so-called bituminous rock deposits are extensive, but they have been developed at only a few places. As described by H. W. Fairbanks, (Fairbanks, H.W., U.S. Geological Survey Folio 163)

" The bituminous rocks are sandstone beds lying near the base of the diatomaceous shale, which is referred to as the Monterey. Most of the sandstone beds which immediately underly or are intercalated with the diatomaceous shale of this locality are more or less bituminous. The structure is monoclinal, with a gentle southwest dip, hence the asphaltic-bearing strata crop out along the sides of the southwestward-flowing streams, where these have cut down nearly or quite to the bottom of the shale.

The zone of the bituminous rock is exposed near the base of the diatomaceous shale from Santa Cruz northwestward as far as the western side of the Big Basin, a distance of more than 20 miles. Throughout this distance the dip of the lower part of the diatomaceous shale and of the immediately under lying sandstone is gently to the west and southwest. At many places through this district the sandstone beds are more or less bituminous, but at only one locality have they been found to be of commercial value."

City Streets Improvement Company's Mine

Under various names, including Walrath Mines, Pacific Improvement Company's Mine, Santa Cruz Bituminous Rock Mines, and more recently City Streets Improvement Company's Mines, this property has been operated for more than 35 years. Operations have been on a reduced scale in later years, the City Streets Improvement Company having gone out of business and control of the property passed to the Bank of California, N. A., San Francisco. Since February, 1923, it has been operated under a working agreement by T. W. Moore, Box 433, Santa Cruz.

The property contains 479 acres, located low down on the southern slope of Ben Lomond Mountain at an elevation of 800 to 900 feet. The workings are three miles northeasterly from Gordola, the shipping point on the Davenport branch of the Southern Pacific, and about five miles in an airline northwest of Santa Cruz.

There are three distinct beds of bituminous sandstone lying practically horizontal on the property. The lower stratum is about seven feet thick and has not been developed to any extent, as work has been confined to the upper and heavier beds. About eight feet of sand, containing a very low percentage of bitumen, separates the lower bed from the middle one. The latter is a rather coarse-grained sandstone averaging 30 feet in thickness containing from 10% to 14% of asphalt. The 'soft' Bituminous rock is mined from this bed. Above this there is a bed of diatomaceaus shale 50 to 60 feet in thickness, on top of which is the upper stratum of bituminous sandstone. The upper bed is a little thinner than the middle one, varying from 6 to 22 feet in thickness. It is finer-grained and harder, but contains from 14% to 18% asphalt. The 'hard' rock is mined from this bed. In use, a varying mixture of the 'hard' and 'soft' rock is used, according to the character of the work.

In early days the material was hauled to the loading station at Gordola by an immense steam tractor, hauling four or five large trailers with solid wooden car wheels holding ten tons each. Much of this old equipment is still on the property.

At the present time the bituminous sandstone is mined by boring holes with augers, and blasting; the large pieces being broken to man-size with sledge and chisel. It is then loaded on 2-ton cars by hand and trammed to a loading bunker from which it is taken by 5-ton trucks to Gordola.

Many thousands of tons of this material have been produced here in the past 35 years; the entire top of Rattlesnake Hill having been cut down to a level floor representing the base of the middle bed of bituminous sandstone. The beds are still exposed in open cuts for over 1000 feet on adjoining hills, and an immense tonnage still remains readily accessible. When properly placed, the excellency of this material has been demonstrated by pavements laid 30 years ago which is still in good condition. Two to five men are employed.


State Mineralogist's Reports XII, p. 28; XIII, p. 43; XVII, pp. 230-232; XVIII, p. 228.

U. S. Geol. Survey 22d Annual Report, Part 1, pp. 384-394;

Santa Cruz Folio 163;

California Journal of Technology, August, 1913.

Cowell Mine

This quarry is situated six miles northwest of Santa Cruz on the extensive land holdings of the Henry Cowell Lime and Cement Company, owners. It is about one-half mile east of the City Streets Improvement Company's Mine, but on the opposite side of Baldwin Creek, which necessitates hauling direct to Santa Cruz for shipment. It has only been worked occasionally in a small way, and was idle at the time of visit.


State Mineralogist's Reports X, p. 621; XII, p. 28; XIII, p. 44; XVII, p. 230; XVIII p. 228.

U. S. Geol. Survey 22d Annual Report, Part 1, pp. 399-404;

Santa Cruz Folio 163

Thurber's Mine

This property is north of and adjoining the City Streets Improvement Company's Mine. The bed of Bituminous sandstone here varies from 10 to 30 feet in thickness. It has not been extensively developed. Idle. Owner, Consolidated Bituminous Rock Co., Nevada Bank Building, San Francisco.


State Mineralogist's Reports VII, P. 96; VIII, p. 554; XII, p. 29; XIII, p. 44; XVII, p. 232; XVIII, p. 228

U. S. Geol. Survey 22d Annual Report, Part 1, pp. 393-396

Santa Cruz Folio 163

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Bituminous Rock   Gold Mineral Water
Black Sand Granite Moulding Sand & Peat
Cement Iron Petroleum & Potash
Clay Lime Stone Industry
Coal Limestone   

The Mineral Survey of Santa Cruz County was printed in the Santa Cruz Chamber of Commerce Annual Report, 1926. Reproduced by permission of the Santa Cruz Area Chamber of Commerce.

View similarly tagged articles:

Ben Lomond Mountain, geology, Henry Cowell, mining


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