Sedimentary Geology, 49 (1986) 193-200 193 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands PEDESTAL ROCKS IN THE PLIOCENE pLrYE FORMATION, NEW MEXICO BRUCE W. NOCITA Department of Geology, University of South Florida, Tampa, FL 33620 (U.S.A.) (Received November 25, 1985; accepted for publication March 5, 1986) ABSTRACT Nocita, B.W., 1986. Pedestal rocks in the Pliocene Puye Formation, New Mexico. Sediment. Geol., 49: 193-200. Pedestal rocks generally form in sandstone/shale terrains, with differential erosion producing a sandstone cap on a shale base. A different type of pedestal rock occurs in the late Pliocene Puye Formation in north-central New Mexico. Here, coarse conglomerate forms the base, and large, detrital boulders form the cap rocks. The formation of these pedestal rocks is dependent on the presence of a minimun amount of conglomerate in the base to provide the necessary support strength for the boulder caps. INTRODUCTION Rocks consisting of a larger residual or erosional rockmass resting on a smaller base or pedestal have been called various names including mushroom rocks, zeuge, toadstool rocks, hoodoo rocks, and gara. The general term used to describe these features is pedestal rock. These natural monuments are generally considered to be the product of differential weathering and erosion, such that the more resistant cap rock rests on a less resistant, slender column. The cap rock is commonly sandstone or conglomerate and the pedestal finer-grained, shaley rock. The cap rock is a remanent of an originally more extensive unit and its size and shape are the product of the surficial processes that formed the pedestal rock. The late Pliocene Puye Formation in northern New Mexico is a coarse-grained alluvial-fan deposit (Griggs, 1964; McPherson et al., 1984, 1985) which contains boulders up to 3 m in diameter. In Rendijo and the upper portion of Guaje Canyons there is spectacular development of pedestal rocks consisting of 1-3 m diameter detrital boulders capping pedestals composed mostly of pebble and cobble con- glomerate. This report documents the occurrence of these somewhat unique geomor- phic features and discusses possible modes of their formation as well as their potential use in sedimentological analysis of the unit. 0037-0738/86/$03.50 © 1986 Elsevier Science Publishers B.V.