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I am born, raised and living in the Columbia Basin of Washington State which has been quiet geologically for a while also (notwithstanding certain Cascade volcanoes which tend to dump a lot of ash here). But you never know when basin activity will pick up (geology and weather).

There were periods of quiescence between major extrusive events...The flows were extruded from vents and northwest-trending fissures east of Pasco and in the southeast corner of the state... The flows were extremely fluid, and as a result a number of them reached the Pacific Ocean via the ancestral Columbia River drainage...The Columbia Basin was the scene of the greatest catastrophic floods ever documented in the geologic record. The Pleistocene Cordilleran ice sheet advanced south into Idaho, damming the Clark Fork River at the Montana border. A huge impoundment, called Lake Missoula, formed.

(later it let go).

The Missoula Floods were big, but the Bonneville Flood released nearly 1,000 cubic miles of water. At its greatest extent, the Bonneville Lake level was 5,090 feet above sea level -- nearly 1,000 feet higher than the current level of Great Salt Lake. When the alluvial dam at Red Rock Pass let go, it unleashed a flood with a volume twice as large as the biggest Missoula Flood. However, unlike the Missoula Floods, the Bonneville Flood occurred over a period of several weeks approximately 17,400 years ago.

That's why you find very little topsoil on the high plateau around Twin Falls -- barren rock everywhere.

So Southern Idaho may not be ideal if you can't swim. Just keep a close eye for any upcoming ice ages and retreat of glaciers.