As one drives easterly on Ygnacio Valley Road across Lime Ridge northwest of Mount Diablo, scars from open pit quarry operations can be seen to the right of the road. To the left is a tall smokestack in an area that in past years was called Cowell but which is now part of Concord. This was the site of the Cowell Lime and Cement Company that produced Portland cement from 1905 to 1946. The cement plant was one of the largest employers in the area in the early 1900's.

The rock was quarried in the Lime Ridge area and carried on a narrow gauge railroad, or by truck, to the Cowell plant where it was crushed, mixed with clay, and then converted to cement in roasting kilns. Sacked cement, which was marketed as "Mount Diablo Cement", left Cowell daily on the company's standard gauge Bay Point and Clayton Railroad, At Bay Point, the cars went on their way to other areas via Southern Pacific, Western Pacific, or Santa Fe railroads.

Through the years farmers threatened to sue the Cowell plant over the air pollution which coated their vines and orchards with fine cement dust. The cement company built a 235-foot-high smokestack in 1934 in an effort to dissipate the dust into the atmosphere. Labor problems forced the plant to close in 1946. The plant was later torn down and the smokestack and quarries are all that remain of this once-thriving industry.

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The rock quarried at Lime Ridge and used to make cement is called travertine, It is the same composition as limestone - almost pure calcium carbonate. The rock is hard, sometimes shows banding, and is colored a light tan by the inclusion of a small amount of iron oxide. Cave formations are formed from the same kind of material. The travertine at Lime Ridge formed, probably in fairly recent geologic time, from circulating waters carrying calcium carbonate in solution which came to the surface through a very porous sandstone called, by geologists, the Domengine formation of Eocene age (about 50 million years old). The water evaporated, leaving behind the travertine which formed a layer on top of the sandstone that originally covered an area 2.5 miles long and 0.5 miles wide and varied in thickness up to a maximum of 20 feet. The Domengine sandstone is exposed in the light-colored quarry faces and can also be seen in the large roadcut just east of the entrance to Cal. State Hayward.