Perris Block

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The Perris Block is the central block of three major fault-bounded blocks of the northern part of the Peninsular Ranges. The Perris Block lies between the to the west and the to the east.[1] The Perris Block, was named by in 1925 for the city of Perris, located near the center of the block.[2]

Structurally stable for millions of years, the Perris Block is an internally unfaulted, eroded mass of Cretaceous and older granitic rocks of the and metasedimentary basement rocks. These rocks compose various ranges of mountains and hills and monadnocks and underlie the valleys within it. It is bounded on the west by the Chino Fault and Elsinore Trough, on the east and northeast by the San Jacinto Fault Zone including the San Jacinto Valley graben. It is bounded on the north by the , in the San Bernardino Valley and in the Pomona Valley. To the south, the Perris Block is bounded by the San Felipe Fault Zone between it and the Temecula, , and sedimentary basins that lie between Temecula and Anza.[3][4] The interior of the Perris Block has various low bedrock mountains, hills and bedrock plains with intervening sediment-filled valleys, that make up six erosional surfaces sculpted by the effects of the vertical oscillation of the block during the Plio - Pleistocene era.[5][3]

Northern Perris Block[]

The northern part of the Perris Block lies north of the Santa Ana River. Here in the Pomona Valley and San Bernardino Valley it has been mostly buried by the sediments from the Transverse Ranges as they rose over the last 2-3 million years. Exceptions are the Jurupa Mountains and Pedley Hills that still rise above that deposition. The now obliterated Slover Mountain also did so before it was mined out of existence. These sediments under the Pomona and San Bernardino Valleys form the aquifer.

East of the Santa Ana River lie the La Loma Hills, Box Springs Mountains and northeastward of them, across the canyon of and of the Pigeon Pass Valley, the range of mountains formed by , Reche Summit, and the Kalmia Hills that border the northeast edge of the Perris Block along the San Jacinto Fault Zone to the Perris Plain.

Central Perris Block[]

The western side of the central Perris Block and across its width eastward south of the Santa Ana River, is bordered by the range of the Temescal Mountains. They run southeastward along the Elsinore Trough to the Temecula Basin. Eastward, these mountains run to the south of the Santa Ana River to , bordering on the Box Springs Mountains. They enclose the Gavilan Plateau and partially enclose the on the west, south and east. They extend their ancient eroded surfaces eastward to the and the Plains of Leon, which they border on the west, southward to the Temecula Basin.

Perris Plain[]

The , an uplifted peneplain, is drained primarily in the , the San Jacinto River watershed flowing into Lake Elsinore, that is dotted by monadnocks and by several other ranges of mountains and hills. Above the San Jacinto Basin, the northwest corner of the Perris Plain is drained by Sycamore Canyon and into the Santa Ana River. Below the San Jacinto Basin, the Perris Plain is bounded on the south by the Plains of Leon, which continues the plains of the Perris Block and by the mountains of the southern Perris Block.

Plains and Valleys of the Perris Block within the San Jacinto Basin:

Mountains and hills of the Perris Block within the San Jacinto Basin include:

Southern Perris Block[]

The Perris Block south of the Perris Plain and San Jacinto Basin is characterized by the extension of the Perris Plain, the Plains of Leon that includes within it the and western , the upper part of the valley of Warm Springs Creek and connecting tablelands, French Valley, and .[6] The southern Perris Block also includes the hills and mountains to the east and south of the Perris Plain, that with the Plains of Leon are all drained by the creeks tributary to the Santa Margarita River into the Temecula Basin.

, drains the Rawson Mountains (south of Diamond and Domenigoni Valleys),[7] , the western slopes of , the , the Tucalota Hills and into Lake Skinner then to Warm Springs Creek, a tributary of Murrieta Creek.[8] The west slope of the southern Magee Hills, and the north slope of the Black Hills are drained by or its tributaries, another Murrieta Creek tributary. , , the west and south slopes of the Black Hills are drained by Temecula Creek or its tributaries, as are the south slopes of Red Mountain, and .

References[]

  1. ^ Earth Resources Technical Report PREPARED FOR: RIVERSIDE PUBLIC UTILITIES BY: POWER ENGINEERS, INC, June 2010, p.3
  2. ^ Walter Atheling English, Geology and Oil Resources of the Puente Hills Region Southern California, Geological Survey Bulletin 768, U.S. Government Printing Office, 1926.
  3. ^ a b Morton, D.M. and Matti, J.C., A vanished late Pliocene to early Pleistocene alluvial-fan complex in the northern Perris block, Southern California. In Conglomerates in Basin Analysis: A Symposium Dedicated to A.O. Woodford, (I.P. Colburn, P.L. Abbott and J. Minch, eds.), Pacific Section S.E.P.M., 1989, Vol. 62, p. 73-80.
  4. ^ Greg T. Cranham (1999). Water for Southern California: Water Resources Development at the Close of the Century. fig. 3 Regional geologic map (modified from Woodford et al, 1971. San Diego Association of Geologists. pp. 45, 46. ISBN 978-0-916251-51-2.
  5. ^ Alfred O. Woodford, JOHN S. SHELTON, DONALD O. DOEHRING and RICHARD K. MORTON, Pliocene-Pleistocene History of the Perris Block, Southern California, Geological Society of America Bulletin, 971
  6. ^ U.S. Geological Survey Geographic Names Information System: Buck Mesa
  7. ^ [Greg T. Cranham, editor, Water for Southern California: Water Resources Development at the Close of the Century, San Diego Geological Soc, Dec 1, 1999 - pp. 43-44, 44 fig. 2 Project Features Map, 47-49, 47 fig. 2]
  8. ^ "Murrieta Creek". Geographic Names Information System. United States Geological Survey.

Coordinates: 33°51′9″N 117°15′19″W / 33.85250°N 117.25528°W / 33.85250; -117.25528

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