Land subsidence and tectonism, Raft River Valley, Idaho

A comparison of 1974 leveling data with elevations established 40 years earlier reveals two types of vertical ground movement which have occurred in Raft River Valley, Idaho: (1) regional differential movement of about 0.22 ft (6.4 cm), apparently due to tectonism, and (2) extensive land subsidence of as much as 2.61 ft (0.80 m) caused by withdrawal of ground water. Data are too sparse to calculate the magnitude or areal extent of subsidence; however, tentative lines of equal subsidence suggest that the area affected by subsidence probably exceeds 100 mi² (260 km²).

In order to estimate historic subsidence or subsidence potential in Raft River Valley serious consideration should be given to a field program of basic-data collection. Leveling along a few carefully selected lines of existing control and the installation and operation of extensometer water-level recorders in areas of continuing water-level decline would provide useful data for evaluating past and estimating future subsidence.