Don R. Mabey

Interpretation of a gravity profile across the western Snake River Plain, Idaho

The gravity and magnetic anomalies over the western Snake River Plain suggest that the plain is underlain by a layer of dense magnetic rock that may be the Miocene Columbia River Basalt Group and by a thin upper crust. The western Snake River Plain may have formed as a rift in Miocene time in response to northeast lateral spreading with the accumulation of more than a kilometre of basalt in the rift. The plain apparently is now in approximate isostatic balance with adjoining highlands.

Giant Desiccation Fissures on the Black Rock and Smoke Creek Deserts, Nevada

Open fissures, from 100 to several hundred feet apart, that have produced polygonal patterns on the Black Rock Desert, Nevada, are believed to be giant desiccation cracks resulting from a secular trend toward aridity in the last few decades. Similar features on the Smoke Creek Desert probably have the same origin.