16 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1907. 



pebbles, or fine gravelly material. In limited areas the accumula- 

 tion of cobbles and gravel in the surface is sometimes excessive, due 

 to the removal of the fine earth by wind action or by erosion. 



Although the soil is of a heavy tenacious character, the finer clay 

 material is generally flocculated; which condition, together with the 

 large quantity of gravel, renders the soil friable, readily cultivated, 

 and capable of maintaining an excellent tilth. 



A compact and usually adobelike heavy loam of deep-red color, 

 carrjang a moderate quantity of gravel, usually underlies the soil at 

 a depth of 6 to 15 inches or less. Beneath this, at a depth of 18 

 inches to 5 feet, a partially indurated hardpan, of deep-red color 

 sometimes mottled with patches of light-gray clay, is found, although 

 in some places the heavy loam may extend to a depth of 6 feet. 

 The hardpan carries a large quantity of rounded gravel and cob- 

 bles, sometimes becoming very dense and hard and resembling con- 

 glomerate rock. Outcrops of tliis material occur along eroded sur- 

 faces or as ledges bordering ravines and gulches carved by intermit- 

 tent streams. Upon the other hand, it often consists entirely of 

 partially indurated or cemented fine claylike material of a soft 

 nature, quite readily penetrated by roots, and frequently easily 

 broken up by the fingers. 



The Redding gravelly loam, which is the prevailing soil of the 

 uplands and the most extensive tjY>e of the survey, occurs as large 

 bodies occupying much of the northern and western parts of the 

 area, although smaller and irregular bodies are found in various other 

 parts of the uplands. It is of considerable extent upon the higher 

 ancient valley plains and lower foothills bordering the more recent 

 valley of the Sacramento River. The surface is usually gently roll- 

 ing or gently sloping, often minutely dissected by deep narrow 

 ravines and gulches in wliich flow intermittent streams. It usually 

 supports a moderately heavy growth of scrub pine, oak, and cha- 

 parral brush of the mountains and foothills, mainly ceanothus and 

 manzanita. 



The soil is generally well drained, except in local depressions 

 where percolation is liindered by underlying hardpan. The cost of 

 clearing is sometimes liigh, but is often nearly repaid by the value of 

 the wood removed. 



The Redding gravelly loam is derived from early Pleistocene allu- 

 vial material deposited in the older Sacramento Valley to a great 

 depth. Owing to its friable structure and heavy subsoil, the Redding 

 gravelly loam has great water-holding capacity. This condition is 

 important and should be augmented by frequent cultivation and the 

 maintenance of a loose surface-soil mulch. Upon the other hand, 

 in some places presence of more or less impervious hardpan strata 

 near the surface arrests percolation of rainfall and decreases the 

 water-holding capacity of the soil. Where the hardpan is very com- 



