14 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1907. 



The soils of this part of the area are derived mainly from the Red 

 Bluff formation. This formation has a maximimi thickness of more 

 than 200 feet and consists of clays, sands, gravels, and cobbles, repre- 

 senting alluvial material deposited over the valley by the Sacramento 

 and its tributary streams in former times, subsequent uplift having 

 elevatetl the valley and caused the carving of the more recent stream 

 valleys. In the vicinity of the Cow Creek Valley small areas of the 

 ui)land soils are derived largely from volcanic tuff, ranging in char- 

 acter from light gray and often pumiceous dust and finely abraded 

 material to andesitic bowlders, the finer material predominating 

 upon the western side of the valley. '^ 



Considerable modification in the soil material derived from the 

 Red Bluff formation has recently taken place by the weathering of 

 the gravels, which are frequently so well decomposed as to be readily 

 broken up with a light blow or crushed with the fingers. In parts 

 of the upland plains exposed to the winds much fine material has 

 been blown away, with consequent concentration of the coarser soil 

 particles and gravels at the surface. 



The formation of the hardpan, of general occurrence in this group 

 of soils, has taken place subsequently to the original deposition of 

 the soil material. It is due to concentration of the finer clay parti- 

 cles in the subsoils by percolating waters and to the partial cement- 

 ing of this claylike material by mineral salts, largely silicates and 

 other salts of iron. 



This hardpan is red to yellowish-gray in color, from a few inches 

 to several feet in thickness, and is usually found at a depth of 18 

 inches to 5 feet, although it may occur at greater depths or, upon 

 the other hand, even outcrop at the surface. It may consist entirely 

 of fine material or of a mass of gravels and cobbles inclosed and held 

 together by the finer material. 



Three types of soil occur in the uplands — the Redding gravelly 

 loam, the Redding loam, and Rough stony land. These soil types 

 merge gradually into one another and into other adjacent types. 

 The separating of these soils was therefore more or less arbitrary. 

 The soil types differ widely in adaptation to crops and in agricul- 

 tural value, depending upon adaptability to and the facilities for 

 irrigation, and the occurrence, character, and position of the hardpan. 



The soils of the valley slopes consist of three types — two of the 

 Anderson series and one local type, the Bellavista sandy loam. 

 They usually are found adjacent to the soils of the uplands, occupy- 

 ing the higher valley slopes, flat-bottomed gulches, and the valleys of 

 intermittent streams. They are usually gray to reddish gray in color, 



oFor further description ot this formation and other geologic features, see Redding 

 Folio, Geologic Atlas of the United States, published by the U. S. Geological Survey. 



