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Figure 21. This seismic line and cross-section, by geophysicist Ray and geologist Keefer, explain much of Rocky Mountains geology, in the writer’s opinion. Large mountain-forming thrusts, as the one on the right, have created mountain ranges scattered throughout the region. These mountain ranges depress the crust, forming basins in front of them. In between the ranges, thrusts of lesser throw (“auxiliary” thrusts) created the anticlines that produce oil and gas, and faults of even smaller throw affect the stratigraphy. Note the Madden thrust just in front of the range-forming Owl Creek Mountains thrust.