GEOLOGY/GEOGRAPHY

bill bonnichsen geologistThe "Borderlands" area is a transition zone between two huge geologic regions…the Basin and Range Province of Nevada and Utah and the Snake River Plains Province of Idaho. The Jarbidge mountains of Nevada are the highest in the northern part of the state with several peaks over ten thousand feet high. The Snake River Plains meanwhile are much lower and stretch for more than a hundred miles to the north toward Twin Falls and Boise, Idaho. Bill Bonnichsen has been exploring this area for nearly six decades, much of that as a member of the Idaho Geological Survey. He says it’s one of the world’s great areas for studying volcanism. Now retired, Bonnichsen continues to pursue his passion for unlocking the geologic story of the region.

plateau and canyons“To the north of the Jarbidge region is the Snake River Plain Volcanic Province, and the Snake River Plain Volcanic Province is a product of North America moving southwestward over a stationary hot spot deep within the earth.

Large amounts of volcanic rock came up from deep in the earth and melted major parts of the earths crust, and caused enormous volcanic eruptions which spewed rhyolite all around the countryside. After that had cooled off it had sunk back down in the ground so it assumes a relatively low profile. It forms a plateau region that's been incised by the canyons of such rivers as the Bruneau and Jarbidge rivers... Over the course of a few millions years the canyons were incised deeply into the volcanic plateau that had been left there.”

scenic peaks"To the south extending from about the Idaho-Nevada border on down through Nevada is what geologist have referred to as the Basin and Range province. And it is characterized by a number of large, high mountain ranges that trend north-south. These mountain ranges were produced along faults as the earth's crust was stretched from east to west...

The Jarbidge Mountains are composed mainly of an igneous rock type called rhyolite; it's the product of volcanic eruptions. In the Jarbidge Mountains the rhyolite is almost a mile thick. The eruptions took place about16 million years ago... Then, at some point in time a few million years later, during the evolution of the Basin and Range Province major faulting occurred along the flanks of the Jarbidge Range and it was uplifted to a much greater height than it had been. Subsequent erosion has carved it into a series of magnificent peaks.”

--Bill Bonnichsen, Idaho Geological Survey (retired)--