The Lower Cretaceous "D" sand in western Adams and Arapahoe Counties, Colorado. contains significant hydrocarbon reserves in stratigraphically trapped reservoirs. Reservoirs are developed in marine bar-type sand stones and in deltaic distributary channel sandstones. Trapping conditions include classical stratigraphy traps consisting of up-dip pinchout of sandstone, and more complex traps such as interchannel point bar porosity permeability pinchout flaps. Recognition of the environment of deposition of individual sand bodies combined with a practical mapping technique utilizing log shape/structure maps should lead to more discoveries in this area.