The Turner Valley field is comprised of two Laramide structures, the Turner Valley and Millar- ville thrust sheets, the latter over-riding the down-plunging north extension of the former. The ancestral fold and age of accumulation are pre-Jurassic and pre-Blairmore. The reservoir rock is a dolomitic biostrome identified by the abundance of detrital crinoids et cetera which form the porous zones and provide source. This relationship between the early accumulation and the age of folding, together with the organic origin of the reservoir, is significant in prospecting for oil in the Mississip- pian rocks of the foothills.