Forreston Dome

Part of the Plum River Fault Zone

Location

West-central Ogle and east-central Carroll Counties (A-4)

References

Kolata and Buschbach 1976, Kolata et al. 1983

Description

The Forreston is an asymmetrical dome located on the south (upthrown) side of the Plum River Fault Zone (fig. 37). It is approximately 10 miles (16 km) long from east to west and 7 miles (11 km) wide. The dome has closure of about 175 feet (43 m) on the Ordovician Glenwood Formation and closure of more than 200 feet (61 m) on the Cambrian Franconia Formation (Kolata et al. 1983). The north flank, adjacent to the Plum River Fault Zone, is steep. Minor faulting has been mapped near the crest of the dome.

Figure(s)

Figure 37   The Plum River Fault Zone and related structures, northwestern Illinois. Structure contours on top of the Glenwood Formation (Middle Ordovician). After Kolata and Buschbach 1976. Contour interval is 50 feet.