SOIL SUEVEY OF SOLOMONSVILLE AREA, ARIZONA. 11 



MARICOPA GRAVELLY LOAM. 



The areas of the Maricopa gravelly loam consist of remnants of the 

 original foot slope of the mountains. The depth of this soil, except 

 in the vicinity of eroded areas where it may be underlain by a calcare- 

 ous hardpan, is always at least 6 feet, and often much greater. 



The Maricopa gravelly loam consists of a chocolate-brown loam of a 

 rather compact, tine, silty texture, containing a considerable propor- 

 tion of tine, angular gravel. The soil usually becomes somewhat 

 heavier in the lower part of the profile. In exposures in the cuts and 

 washes so common in areas of this soil the subsoil is frequently seen 

 to be of a very heavy, compact nature, cracking upon exposure to the 

 weather and resembling adobe. The fine earth material of this soil is 

 somewhat heavier in this than in other areas where it occurs. 



Before cultivation the surface of the soil is compact, smooth, and 

 often thickly strewn with small gravel, usually quite well rounded. In 

 local spots this gravel is almost entirely of volcanic origin, often partly 

 embedded in the soil and imparting a peculiar^ hard, smooth, glistening 

 surface, but the particles are of small size and would not interfere with 

 cultivation. The soil becomes quite sticky when wet and bakes some- 

 what when puddled and dried. Along the margins of the cuts, washes, 

 and terraces, and over portions modified by erosion, the gravel is larger 

 and the quantit} 7 greater, and the soil becomes lighter and more sandy 

 by loss of the finer particles through erosion. A great part of this 

 area along the terraces, or in places of severe erosion, is rendered very 

 difficult or impossible of cultivation by excess of gravel. Strata of 

 very hard and refractory hardpan, similar to that occurring in the 

 " Mortar Beds" of the Tertiary gravels of the Great Plains in eastern 

 Colorado (see Soil Survey in the Arkansas Valley, Field Operations of 

 the Bureau of Soils, 1902), also occur in the subsoil of these terrace 

 and eroded areas. Each strata probably represents the upper limit of 

 the water table at some time during the earl} r history of the valley. 



Areas of the Maricopa gravelly loam occur on the upper terraces 

 throughout the area surveyed, generally forming the borders of the 

 cultivated valley lands. Areas also occur upon the mesa lands. The 

 surface, except where eroded, is level or gently sloping. These lands 

 are, however, often cut by narrow canyons from 25 to loo or more 

 feet in depth, with steep or nearty vertical walls. Small domelike 

 elevations or hills, with surface thickly strewn with cobbles and gravel, 

 frequently occur in the vicinity of the canyon mouths. 



Small seepage springs, alkaline in character, sometimes occur along 

 the margins of the terrace borders upon the northern and eastern sides 

 of the valley. Fairty good natural drainage is, however, usually 

 afforded by underlying gravel beds. 



This soil is derived from the weathered debris of the rocks of the 

 surrounding mountains. During the processes of valley filling this 



