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Alluvial Fans and Near-Surf Ace Subsidence in Western Fresno County California

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Alluvial Fans and Near-Surf Ace Subsidence in Western Fresno County California Alluvial Fans and Near-Surf ace Subsidence in Western Fresno County California GEOLOGICAL SURVEY PROFESSIONAL PAPER 437-A Prepared in cooperation with the California Department of Water Resources Alluvial Fans and Near-Surface Subsidence in Western Fresno County California By WILLIAM B. BULL STUDIES OF LAND SUBSIDENCE GEOLOGICAL SURVEY PROFESSIONAL PAPER 437-A Prepared in cooperation with the California Department of Water Resources. A study of compaction caused by water percolating through certain alluvial-fan deposits for thejirst time since burial. UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library catalog card for this publication appears after page A71. For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 FOREWORD Subsidence of the land surface occurs in three extensive areas in the San Joaquin Valley and in the peat lands of the Sacramento-San Joaquin Delta at the north end of the valley. Subsidence hi the three valley areas is related mainly to progressive lowering of the artesian head in confined aquifers. In the Los Banos-Kettleman City area, largely in western Fresno County, more than 1,100 square miles has subsided at least 1 foot, and maximum subsidence in 1960 was about 22 feet. The maximum yearly rate of subsidence is about 1 foot. Locally, on the western and southern flanks of the valley, subsidence also has followed application of irrigation water to certain deposits of subnormal moisture content above the water table. This near-surface subsidence, which exceeds 10 feet in places, is superposed on the subsidence due to compaction of the aquifer system beneath. The character, extent, and rate of the subsidence in the valley are described in prelimi­ nary form in an earlier report (Inter-Agency Committee, 1958) and are being described in detail in U.S. Geological Survey reports now (1964) in preparation. Subsidence poses serious problems in the construction and maintenance of engineering structures, especially in large canals for water transport, but also in irrigation distribution systems, pipelines, roads, and drainage systems; it also affects land use. Two existing large canals pass through subsiding areas, and the authorized California aqueduct of the State and the San Luis project canal of the Bureau of Reclamation will pass through many tens of miles of subsiding ground. Thus, the extent, magnitude, and rate of past subsidence and the expected amount of future change in altitude of the land surface are-of paramount impor­ tance in the planning, construction, and maintenance of such major structures. Compaction of aquifer systems, the principal factor in the subsidence, also has an effect on the ground- water yield and causes casing failures. Because of the problems in water development and distribution caused by subsidence, the Geological Survey in cooperation with the California Department of Water Resources began a study of these subsiding areas in 1956. The objectives of this study are: 1. To provide vertical control on the land surface to measure the extent, rate, and magnitude of subsidence (a vital supporting program by the U.S. Coast and Geodetic Survey). 2. To determine causes of the subsidence, the part attributable to different causes, and the depth range in which subsidence is occurring. 3. To estimate the rates and amounts of subsidence that would occur in the future under assumed conditions; to determine whether any part of the subsidence is reversible, and if so, how much; and to suggest any methods that could be used to decrease or alleviate subsidence. The first report resulting wholly from the cooperative program with the State is the following paper by W. B. Bull on "Alluvial Fans and Near-Surface Subsidence in Western Fresno County, Calif." Other reports in progress or planned are: Subsidence due to ground- water withdrawal in the Los Banos-Kettleman City area; a summary report on near-surface subsidence; subsidence in the Tulare-Wasco area; and subsidence in the Arvin-Maricopa area. J. F. POLAND, Research Geologist CONTENTS Page Page Foreword._________________________________________ m Geology of the alluvial fans Continued Glossary._ _________________________________________ vii Alluvial-fan deposits Continued Abstract._ _________________________________________ Al Older depdsits___----___--_----_---_-------- A33 Introduction.______________________________________ 1 Amount and rate of deposition.______________ 36 Purpose and scope._____________________________ 1 Summary of alluvial-fan deposits-____________ 39 Acknowledgments__ _ __________________________ 2 Near-surface subsidence-____________--____-___-----_ 39 Geographic setting______________________________ 2 Inter-Agency Committee on Land Subsidence test- Location and topographic features.___________ 2 plot program.. _ ______________________________ 39 Climate and vegetation____________________ 4 Description of near-surface subsidence.____________ 41 Geology of the alluvial fans__________________________ 5 History of near-surface subsidence. __________---_- 44 Regional geology____ ___________________________ 5 Effect of subsidence on agricultural operations.-.-.- 45 The Coast Range orogeny_______________________ 5 Effect of subsidence on engineering operations.-____ 46 Geology of the drainage basins.__________________ 6 Causes and mechanics of near-surface subsidence- _ _ 48 Geomorphology_ __________________________ 6 Stratigraphy.______________________________ 8 Overburden load_______-__-_____-___------ 48 Geology and vegetation of the Arroyo Ciervo Moisture conditions...______________________ 48 drainage basin_-_-________________________ 11 Significance of clay_________________-----_- 51 Summary of the geology of the drainage basins. 15 Amount of clay__________________----- 51 Geomorphology of the alluvial fans.______________ 16 Type of clay--.--------------.--------- 52 Alluvial-fan deposits. ___________________________ 17 Strength of clay._____________-___---_-- 52 Causes of deposition._______________________ 17 Density of subsiding and nonsubsiding fans_ _ . _ 57 Classification and description_______________ 18 Consolidation characteristics-_____-__-_------ 58 Mudflow deposits__--______.____________ 21 Effect of lithology and salts.______-_____----_ 61 Water-laid sediments__________________ 26 Summary of near-surface subsidence-_____________ 62 Deposits intermediate between mudflows and water-laid sediments._____________ 28 Methods of making grain-size analyses and density tests. 63 Boulders and armored mud balls____________ 29 Preparation of samples for consolidation tests__________ 64 Textural and structural features of alluvial-fan References._ __________---_-_-------_--------------- 68 deposits- ________________________________ 30 Index.__________----_----------------------------- 71 ILLUSTRATIONS [Plates are in pocket] PLATE 1. Geologic map of parts of Fresno, Merced, and San Benito Counties, Calif. 2. Drainage basins, alluvial fans, and subsidence areas (1961). 3. Geologic map of the Arroyo Ciervo drainage basin. 4. Vegetation of the Arroyo Ciervo drainage basin. Page FIGURE 1. Map of parts of Fresno, Merced, and San Benito Counties, Calif., showing area discussed in this paper. A3 2. Average monthly rainfall, 1919-58, at New Idria___________._-__-__------_---------------------- 4 3. Relation of total relief to area of selected drainage basins. __________________-_-------_------------ 7 4, 5. Area-altitude curves for 4. Drainage basins of Moreno Gulch and Panoche Creek,___________________-___---_-_---------- 8 5. Selected drainage basins of subsiding and nonsubsiding fans_________________-----__---------- 9 6. Difference in vegetative cover on the north and south slopes of Arroyo Ciervo___________-_---_-----. 13 7. Cross-valley profiles of the Arroyo Ciervo drainage basin_______________-______--------_-_----_--- 15 8. Nomenclature and grain-size distribution of alluvial-fan deposits-____-_--_--_------_-_------------- 19 9. Mississippi Valley Corps of Engineers nomenclature diagram. _________________-_------------------ 20 10. Grain-size distribution and sorting of alluvial-fan deposits __________________--------__----------- 20 VI CONTENTS Page FIGURE 11. Textural (CM) patterns of the coarsest one pereentile and median grain size of alluvial-fan deposits in western Fresno County________________________________________________________________________________ A21 12. Shape of alluvial-fan deposits_____________________________________________________________________ 23 13. Cumulative curves of alluvial-fan deposits.______________-___-_---__----_-__--------_--__--_________ 25 14. Variation in the grain size and clay content in the downslope direction.________________________________ 27 15. Distribution of boulder trains on an alluvial fan in sec. 27, T. 13 S., R. 11 E__________________________ 29 16. Armored mud balls and desiccation cracks in armored mud balls and shale cobbles_____________________ 31 17. Textural and structural features of alluvial-fan deposits.________-_____-____-_-------______--_________ 32 18. Variation in the grain size and clay content in the downslope direction for samples from 30-foot core holes in the Arroyo Ciervo fan________________________________________________________________________ 35 19. Grain-size distribution of surface and core-hole samples from the Arroyo Ciervo fan____________________
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