SPECIAL ARTICLES.

Detailed technical reports on special subjects, the result of research work or extended field investigations, will continue to be issued as separate bulletins by the Bureau, as has been the custom in the past.

Shorter and less elaborate technical papers and articles by members of the staff and others are published in each number of 'Mining in California.'

It is anticipated that these special articles will cover a wide range of subjects both of historical and current interest; descriptions of new processes, or metallurgical and industrial plants, new mineral occurrences, and interesting geological formations, as well as articles intended to supply practical and timely information on the problems of the prospector and miner, such as the text of new laws and official regulations and notices affecting the mineral industry.

CLAY DEPOSITS OF THE ALBERHILL COAL AND

CLAY COMPANY.

By JAS. H. HILL.

Location.

The clay deposits of the Alberhill Coal and Clay Company, compris ing some two thousand acres of land, are situated at the town of Alberhill, in Riverside County, California, approximately seventy-five miles southeast of Los Angeles. Reference to the accompanying map, Plate 1, will indicate the region directly served by them, and their central location with respect to the many important towns and cities of this district.

The great economic importance of these deposits may be considered to be due to three main factors:

(1) The excellent quality, wide variety, and enormous quantities of the clays available.

(2) The extensive commercial development of the deposits over many years, resulting in cheapness of mining and large-scale production.

(3) The fortunate central location in a densely populated and rapidly growing section.

The portion of southern California served from these deposits has for several years shown an almost unprecedented growth in wealth, population, and commercial development, with a resulting demand for clay products of all kinds far in excess of the ability of local manufacturers to supply. Clay working plants have continually increased their capacities, and many new ones have sprung up in response to the insatiable demand for building materials and pottery wares of all sorts, so that the Los Angeles district is now one of the great clay-working centers of the United States. A great preponderance of the raw material for these plants has been supplied by the Alberhill deposits, owing to their natural advantages in quality of clays and cheap quantity production.

'President, Alberhill Coal and Clay Company.

1

Plate 1. Location of the Alberhill Coal and Clay Company's Deposits
at Alberhill, California.

The occurrence of the Alberhill clays is uniquely favorable, since the deposits comprise an entire small mountain or detached foothill some five miles in circumference, rising abruptly from the floor of the Temescal Valley. The tracks of the Atchison, Topeka, and Santa Fe Railway skirt the base of this hill, closely adjacent to the clay pits themselves, so that the clay may proceed by gravity haulage direct to loading trestles over the rails. Further advantage of the elevation of the clays above the rails has been taken in the mining processes, as will be noted later, with the result that large tonnages are handled at a minimum cost.

General Geology.

"The valley in which these extensive deposits lie was in Tertiary times an arm of the sea opening northward into the valley of western San Bernardino County and extending southerly to Temecula. Its width is from one to two miles, but its depth is unknown, as at the old terra cotta works near Alberhill a drill hole was sunk over 600 feet without reaching the bottom of the basin.""

At the Alberhill pits, the clays present a wide diversity of color, character, and degree of consolidation. An extraordinary variety is found, including silicious fire clays, ball clays, plastic white- and buffburning clays, highly aluminous and very refractory clays, numerous red-burning clays, and an extensive bed of material from which a china clay is obtained by washing. A bed of lignite coal ranging from two to eleven feet in thickness occurs comformably with the clay strata, and adjacent to this the best fire clays are found. The strata are regular

'Clay Industry in California,' Preliminary Report No. 7, January, 1920, California State Mining Bureau.

Photo No. 1. Southwest wall of the Main Pit of the Alberhill Coal and Clay Company. The heavy stratum of clay directly behind the bunker is Main Tunnel Fire Clay. In the background, Plant No. 4 of the Los Angeles Pressed Brick Company, which draws clay direct from the Alberhill pits.