The study was made to determine the subsurface shape and extent of faulting in the section of the Portneuf River valley between Lava Hot Springs and McCammon, Idaho. A series of roughly north-south-trending faults cuts the valley, leading to a stepped bed-rock surface. These steps are downdropped going west from Lava Hot springs to McCammon. Gravity readings were taken on a Worton Gravimeter and adjusted to latitude, terrain, and free air corrections. These final values were plotted and contoured on a 1:24,000-scale topographic map. Cross sections through the contours were then made and the resulting picture interpreted using Nealson's method. Magnetics were conducted to determine the extent of the valley-filling basalt.

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