[1][2][3][4] The basin was formed when the Earth's crust sank along the continental side of the Rocky Mountains during the Devonian Period (about 415 to 360 million years ago).
From that time until the Late Cretaceous Period (about 100 to 65 million years ago), the region was covered by the sea at various intervals.
Uplift the region beginning about 65 million years ago halted sedimentation and exposed the basin deposits to erosional forces.
The organic matter buried under layers of sediment and subjected to intense heat and pressure developed into oil and natural gas, which collected in the surround porous rock (e.g., limestone reef remnants).
Structural traps produced by the folding and faulting of rocks in the basin during the formation of the Rocky Mountains helped promote petroleum accumulation.