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relatively flat , but major folds occur where there has been <br /> post-depositional tectonic activity . Such folding is <br /> evident in the Grand Hogback , the. Little Bookcliffs , the <br /> Uncompahgre Uplift and the Black Canyon of the Gunnison. <br /> Monoclines are the principal structural feature of <br /> the plateau . :Most of the mcnoclines are associated with <br /> uplifts , and represent lines of great vertical shift . <br /> The Grand Hogback lies to the east of the Coal <br /> Basin anticline , which occurs as a small extension at its <br /> southern end . Bedrock units beneath the Coal Basin outcrop <br /> on the Grand Hogback, then dip steeply , far beneath the <br /> mining activity which occurs in the basin . The units are : <br /> the Cretaceous- (Dakota) formation, the Jurassic- (Morrison <br /> formations and Entrada sandstones) , and the Permo-Pennsylvania <br /> (Maroon) formations . <br /> Above the Dakota formation lie younger sedimentary <br /> rocks , which are associated with the Piceance Basin , the <br /> eastward extension of the much larger Uinta Basin of extreme <br /> western Colorado and eastern Utah . The Piceance Basin lies <br /> on the eastern boundary of the Colorado Plateau physio- <br /> graphic province , adjoining the Southern Rocky ifounIain <br /> - <br /> physiographic province . Coal Basin occurs at the southern <br /> end of the Piceance Basin . <br /> The intrusion of Tertiary sills , dikes and laccoliths <br /> has greatly disturbed the area . The Coal Basin anticline is <br /> thought to have been imposed on the Grand Hogback monocline <br /> by a laccolithic intrusion . <br />