The Calvin 28 cryptoexplosive disturbance, Cass County, Michigan
Geophysical data, geologic mapping, and the extensive drilling of oil and gas test wells have delineated a subsurface structure in Calvin Township, Cass County, Michigan, T.7S., R.14W.; Adamsville, Michigan, 7½-minute Quadrangle, The center of the structure is approximately 1 mi (1.4 km) southwest of the village of Calvin Center (Fig.1), 1). The feature maintainsa surface topographic expression and a partially encircling drainage pattern, but its major structural complexity is concealed by drift and Paleozoic rock.
The location of the Calvin 28 cryptoexplosive disturbanceis shown in Figure 1, which uses an idealized geologic map as a base and to which road numbers have been added. The Calvin 28 cryptoexplosive disturbance can be reached by driving 4 mi (6.4 km) east on Michigan 60 from Cassopolis until encountering the intersection of Calvin Center Road. A right (south) turn on Calvin Center Road will take the visitor toward the structure. After traveling 4.2 mi (6.8 km) on Calvin Center Road, thevisitor will cross over the outer encircling rim of the structure. The outer edge of this rim is delineated by a chain of lakes connected by Christiana Creek (Fig.1), 2). Continuing south on Calvin Center Road 0.5 mi (0.8 km), one encounters the village of Calvin Center. The village is located, subtly, within the annular depression surrounding the central uplift of the structure. Continue south an additional 1 mi (1.6 km) to the junction of Calvin Hill Stree and turn right (west). By traveling 0.5