562 



UNITED STATES MINERAL RESOURCES 



diction of future public-works projects. As the 

 Nation becomes urbanized with a high population 

 density, the need for more public-financed dams and 

 highway projects may decrease. New forms of mass 

 transit and housing structures, however, will place 

 increased demands on the sand and gravel industry. 



GEOLOGIC ENVIRONMENTS AND THEIR 

 DISTRIBUTION 



Sand and gravel are unconsolidated rocks and 

 minerals ranging in size from silt (0.0039 mm) to 

 boulders, formed by the breakdown, erosion, and 

 transport of bedrock by ice, water, and wind. The 

 precise definition and specifications for sand and 

 gravel are extremely variable and commonly so 

 complex that generalization is difficult. However, 

 gravel generally has an upper size limit of 314 

 inches in diameter and a lower limit of one-fourth 

 of an inch, and sand particles are 1/4-1/16 of an 

 inch in diameter (Industrial classification of the 

 American Society for Testing and Materials). 



Ideally, a commercial deposit contains 60 percent 

 gravel and 40 percent sand (Goldman, 1961). This 

 provides ample coarse material to crush for road 

 base or bituminous aggregate, and sand in the cor- 

 rect sizes and proportions for use in concrete. In 

 addition, the aggregate used for concrete should be 

 essentially free of clay, silt, mica, organic matter, 

 chemical salts, and surface coatings. 



The primary commercial sources of sand and 

 gravel are along existing or ancient river channels 

 and in glaciated terranes ; marine and lake environ- 

 ments have been less important source areas. Water 

 is the sculpturing, sorting, cleansing, and transport- 

 ing agent that is responsible for the flood-plain, 

 outwash-plain, stream-terrace, alluvial-fan, esker, 

 kame, delta, and moraine deposits that form the 

 principal commercial deposits of sand and gravel. 

 Windblown deposits locally are of minor economic 

 importance. 



The sand- and gravel-rich geologic environments 

 differ throughout the United States. The distribu- 

 tion of the most abundant deposit types on a 

 countrywide geographic basis is as follows: North- 

 ern States, glacial outwash and till; Atlantic and 

 Gulf Coast States, marine terraces; Southeastern 

 and South Central States, river deposits; Mountain 

 States, stream and fan deposits; Great Plains, 

 stream deposits; and Pacific Coast States, alluvial 

 fans, river deposits, river terraces, beaches, and 

 dunes. 



California leads all other States in sand and 

 gravel production, of which 75 percent of the sand 

 and gravel is produced from stream deposits. The 



huge alluvial-fan deposits in both the San Francisco 

 and Los Angeles areas are the main sources of sand 

 and gravel, but stream-channel deposits are also 

 widely exploited. The stream deposits throughout 

 the State are important sources for sand and gravel 

 primarily because of their widespread availability, 

 but other factors, such as thin overburden, nearness 

 to water necessary for processing, and yearly re- 

 plenishment by spring flooding, are important. The 

 average particle size changes along a river channel, 

 generally providing a variety of differently sized 

 material for specific needs. The natural abrasive 

 action prevalent during stream transport removes 

 the nonresistant particles and concentrates the dur- 

 able ones. Stream-produced subrounded to well- 

 rounded particles are particularly desirable for use 

 in concrete. 



Glaciofluvial deposits, eskers, kames, and outwash 

 provide the bulk of the sand and gravel in the Mid- 

 western and Northeastern States. These deposits 

 are favorable sources for sand and gravel because 

 they are common and widespread, possess little 

 deleterious material, and are generally free of over- 

 burden. 



In 1964 only 3 percent of the United States pro- 

 duction of sand and gravel (including shell deposits) 

 came from the ocean floor (Emery, 1966). As land 

 sources are exhausted or removed from production 

 for various reasons, the offshore deposits will prob- 

 ably be more extensively exploited. 



Bedded pre-Quaternary semiconsolidated sand- 

 stones and conglomerates deposited in ancient allu- 

 vial, lake, or marine environments have rarely been 

 used as sources for sand and gravel. This type of 

 deposit, while having a potential advantage of almost 

 unlimited tonnages, has such disadvantages as thick 

 overburden, high content of weathered, friable par- 

 ticles, high percentage of clay, and enough indura- 

 tion to require crushing. The use of such deposits 

 is currently limited, although the Pliocene Kern 

 River Formation in southern California has been 

 utilized as a sand and gravel source (Goldman and 

 Klein, 1961). 



POTENTIAL RESOURC3ES 



The estimated potential resource of sand and 

 gravel in the United States is of little value unless 

 costs of production are considered. A bulk tonnage 

 not only would be difficult to estimate, but also 

 would be meaningless without an economic frame 

 of reference. Considerations, such as location, ton- 

 nage, quality, accessibility, and economic availabil- 

 ity to markets, must be included in meaningful 

 evaluations. In the near future shortages of sand 



