The various processes that affect hillslopes in the Sonoran Desert of southern Arizona vary considerably in relative importance, depending upon elevation (and hence climate), angle of slope, and the nature and weathering properties of the bedrock. Hillslopes on volcanic bedrock generally have fixed surfaces, whereas hillslopes on granitic bedrock have mobile surfaces. The difference is related to the method and rapidity of production of houlders from the bedrock mass. Large boulders on hillslopes below about a 2,000-foot elevation show evidence of past episodes of case-hardening and depostiion of desert varnish, whereas the fragments on slopes above about a 3,000-foot elevation have undergone more rapid or more prolonged mechanical weathering, probably by frost action and chemical weathering, that has destroyed most of the case-hardening and desert varnish. Hillslopes of less than 28.5 degrees on both granite and volcanic rocks are highly stable, whereas those between 28.5 degrees and up to 36.0 degrees are increasingly unstable, and the upper limit of debris-covered hillslopes is approximately the angle of repose of the debris. Debris-covered hillslopes steeper than about 36 degrees are rare and require some additional agency, seldom present under desert conditions, to maintain the surface cover. Steeper barerock slopes are common, however. The two stability limits, 28.5 degrees and approximately 36.0 degrees, are related to the frictional properties of the rock itself. An effort to find a statistical correlation between slope angle and fragment size was largely unsuccessful and it is suggested that the concepts of the boulder-controlled slope and the repose slope be abondoned. /Author/

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  • Corporate Authors:

    University of Chicago Press

    1427 E. 60th Street
    Chicago, IL  United States  60637-2954
  • Authors:
    • Melton, M A
  • Publication Date: 1965-9

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 715-729
  • Serial:
    • Journal of Geology
    • Volume: 73
    • Issue Number: 5
    • Publisher: University of Chicago Press
    • ISSN: 0009-3920

Subject/Index Terms

Filing Info

  • Accession Number: 00263516
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Dec 13 1974 12:00AM