▁recognized ▁twelve ▁years ▁earlier ▁by ▁John ▁New berry ▁in ▁New ▁Mexico , ▁during ▁the ▁I ves ▁expedition ▁of ▁ 1 8 5 7 - 1 8 5 8 . ▁However , ▁the ▁dis ruption ▁of ▁the ▁American ▁Civil ▁War ▁kept ▁his ▁work ▁from ▁becoming ▁widely ▁known . ▁This ▁Great ▁Un con form ity ▁is ▁a ▁regional ▁un con form ity ▁that ▁separ ates ▁the ▁T onto ▁Group ▁from ▁the ▁underlying , ▁fault ed ▁and ▁t ilt ed ▁sed iment ary ▁rocks ▁of ▁the ▁Grand ▁C any on ▁Super group ▁and ▁vert ically ▁fol i ated ▁met am orph ic ▁and ▁ igne ous ▁rocks ▁of ▁the ▁V ish nu ▁Bas ement ▁Ro cks . ▁The ▁un con form ity ▁between ▁the ▁T onto ▁Group ▁and ▁the ▁V ish nu ▁Bas ement ▁Ro cks ▁is ▁a ▁non con form ity . ▁The ▁break ▁between ▁the ▁T onto ▁Group ▁and ▁the ▁Grand ▁C any on ▁Super group ▁is ▁an ▁angular ▁un con form ity . ▁ ▁Pow ell ' s ▁Great ▁Un con form ity ▁is ▁part ▁of ▁a ▁continent - wide ▁un con form ity ▁that ▁extends ▁across ▁Laurent ia , ▁the ▁ancient ▁core ▁of ▁North ▁America . ▁It ▁marks ▁the ▁progress ive ▁sub mer gence ▁of ▁this ▁land mass ▁by ▁a ▁shall ow ▁cr at onic ▁sea ▁and ▁its ▁bur ial ▁by ▁shall ow ▁marine ▁sed iments ▁of ▁the ▁Camb rian - E ar ly ▁Ord ov ician ▁Sau k ▁sequence . ▁The ▁sub mer gence ▁of ▁Laurent ia ▁ended ▁a ▁length y