Figure 4. Ponca City Field, Kay County, Oklahoma. This asymmetric, or compressional, anticline has produced >12 million barrels of oil from multiple horizons. Shear zone mapped by magnetics (blue) lies west of the steep part of the fold mapped on the "Mississippi Lime" (red), indicating a west dip for the underlying blind reverse fault (inset). The west dip on this fault is also shown on seismic data.