Origin and hazard implications of a matrix-free boulder deposit on the east flank of the Organ Mountains, south-central New Mexico
William J. Stone

Abstract:

A boulder deposit on an alluvial fan on the east flank of the Organ Mountains is of special interest due to the large size of the clasts it contains and the lack of any matrix. The boulders are rounded, nearly equidimensional, as much as 10 ft in maximum diameter and composed of igneous rock types. As various aspects of the setting rule out primary matrix-free origins (talus, rock-glacier, boulder-flow or sieve deposition) and transport of such large clasts is unlikely without mud, secondary removal of the finer fraction seems likely. The deposit is, therefore, concluded to be a debris flow from which the matrix has been completely flushed by repeated washings during the larger flow events in the adjacent channel of Ash Canyon. The feature appears to be young, post-dating a Holocene fault whose scarp localized its formation. Such deposits attest to the flashflood hazard in the area.


Citation:

  1. Stone, William J., 1998, Origin and hazard implications of a matrix-free boulder deposit on the east flank of the Organ Mountains, south-central New Mexico, in: Las Cruces Country II, Mack, G. H.; Austin, G. S.; Barker, J. M., New Mexico Geological Society, Guidebook, 49th Field Conference, pp. 75-77.

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