Large landslides, composed of megabreccia, interbedded in Miocene basin deposits, southeastern Arizona

Abstract

The landslides in the Kearny and El Capitan Mountain quadran gles, Final and Gila Counties, Ariz., are tabular or lenslike masses of megabreccia enclosed in Miocene basin deposits. The megabreccias within individual slide blocks are composed of pervasively brecciated Precambrian and younger formations that remain in normal stratigraphic sequence, indicating that each landslide moved as a fairly coherent mass. The megabreccias consist of fresh, mostly angular rock fragments in a comminuted matrix of the same composition as the fragments. The matrix ranges in amount from sparse to abun dant. Where the matrix is sparse, the fragments fit tightly with little or no rotation. Locally fragments are rotated but not moved far; most units within a slide block are lithologically homogeneous.