We neighborhood kids used to call it the "Chalk Mine." To us, the abandoned quarry looked like something out of the Old West. We thought for sure it had been there since cowboy days; maybe even a hundred years! There were a bunch of other tall tales about the place, but it would be another half century before I finally uncovered its factual history. Much was surprising to me. For one thing, the rocks mined there weren't "chalk" at all...
"There was a large deposit of [diatomaceous] earth on Covina Hills Road that the Featherstone Company successfully mined and processed through the 1920s and early 1930s. The operation closed during the Depression. The property was part of the 2,100 acre Hill Ranch that Frank Marion Chapman and E. G. Shouse purchased from the Hollenbeck family of East Los Angeles." --Barbara Ann Hall, Ph.D.1
So, far from being there a hundred years, it turned out the quarry wasn't even as old as my parents. The diatomite itself, however, was actually formed about 7 million years ago, in the upper Miocene epoch.2
Featherstone Quarry (upper right), Covina Hills, 1926. I-10 now passes from l. to r. through the low white hill at center.
'Dick' Whittington Studio, photographer. Courtesy of The Huntington Library, San Marino, CA. Link to full-res image.
The photo above is the only one I know of that shows the quarry when it was still in operation. The diatomaceous earth mined there was used primarily in the manufacturing of tile, pipes and conduits.2
Exactly when quarrying began at Featherstone is not known. Looking at old maps, it can be seen that roads associated with the mine were present in the 1910s, which would be earlier than other accounts. Exactly when quarrying stopped is also uncertain. A geology field report based upon data compiled in 1932 stated that operation of the mine "ceased several years ago,"2 so it may be that Featherstone Quarry did not survive into the 1930s, after all.
The abandoned quarry (right), 1948. Fair use courtesy HistoricAerials.com.
The "Chalk Mine" as seen from our house on Rancho El Encino, June, 1962.3
What we called the "Quartz Mine" can also be seen to the left of center. Inside that cleft was a thick outcropping of crystalline gypsum.
In 1965, all of the ancient hills north of our neighborhood were bulldozed to create the Covina Heights housing development. Almost a mile square, the massive earthmoving project took a year to complete. Our chalk mine and the whole wild rangeland surrounding it were no more...
View of the former quarry site from Rancho El Encino, December, 1968.
The mine may be gone, but 50 years later, many surface deposits of the white diatomaceous earth are still plainly visible.
Treasure! My own specimen of Featherstone diatomite, collected in 2010 in situ from an intact geologic stratum.
1Hall, B.A. (2007) Covina (Images of America). Arcadia Publishing, San Francisco, California. 127pp.
2Harshman, E.N. (1933) Geology of the San Jose Hills, Los Angeles County, California. M.S. Thesis. California Institute of Technology, Pasadena, California. 91pp.
3PS: If any of my old neighbors from the Ranchos has a better picture of the chalk mine than this one, please let me know!