The rocks exposed in the Harrison quadrangle are exclusively sedimentary. They range in age from Early Ordovician to Middle Pennsylvanian and are represented principally by dolostone and limestone, although sandstone, and to a lesser degree shale, are also present. Bedrock outcrops are common, but of limited areal extent. The bedrock is usually covered by a relatively thin layer of surficial materials (soil, residuum, colluvium and (or) alluvium). The stratigraphic nomenclature of the quadrangle is summarized in figure 1.The Harrison quadrangle is in a stable cratonic region on the southwest flank of the Ozark uplift and contains a moderate number of mapped faults. High-angle normal faults and long, narrow grabens are dominant. A northwest trend in the eastern three-quarters of the northern half of the quadrangle changes to east-west and northeast in the western part. In the northeastern part of the quadrangle, discontinuous faults extending from T. 27 N., R. 14-15 W., to T. 24 N., R. 10 W., are along the trend of the Bolivar-Mansfield tectonic zone, which extends into this quadrangle from the Springfield quadrangle to the north (see others, 1991, andKisvarsanyi, 1991). Similarly, in the west-central part of the quadrangle, a sinuous fault extending from T. 23 N., R. 22 W., into T. 21 N. (Missouri), R. 20 W., is approximately along the trend of the Chesapeake tectonic zone in the Springfield quadrangle. Structures in Canadian post-Roubidoux Formation units are difficult to discern because of the great thickness of the units and the lack of good marker beds. In the southern half of the quadrangle, two major faults and at least one minor fault are discernible; major structural trends are northeast and east-west, and a minor west-northwest trend is apparent.This map is the product of two different state geological surveys whose approaches to geologic mapping and interpretations of regional stratigraphy are similar but not identical as are the rocks themselves. In particular this is true of the Lower Mississippian strata, which in Missouri are divisible into two mappable units but in Arkansas are lumped as the Boone Formation (see fig. 1); the lower part of the Boone, designated in Arkansas as the St. Joe Limestone Member, consists of the same four units as the lowermost Mississippian in Missouri, but is too narrow in outcrop width to be mapped separately. Consequently the Description of Map Units that follows is divided into two sections, one for Missouri and the other for Arkansas. "State-line" contacts at the Missouri-Arkansas border are artificial and indicate only the change in map units, not a change in the nature of the rocks.