Idaho's potatoes grow on top of an old lava plain. But that plain is hiding something else — a huge amount of water, moving slowly through the rock. And where a canyon cuts the rock open, the water comes out sideways.
The Snake River Plain is built out of basalt — layer upon layer of old lava flows, full of cracks and holes. Rock like that can soak up and carry enormous amounts of water underground. A big underground store of water like this is called an aquifer.
Basis: Geology and hydrology: the Snake River Plain is underlain by fractured basalt lava flows and sediments, and that basalt holds a large, highly productive regional aquifer (USGS studies of the Snake River Plain aquifer system).
The Snake River has cut a deep canyon straight into that rock. Where the canyon wall slices through the water-filled layers, the aquifer does not wait for a river to carry it — it pours out of the cliff face as springs. One stretch of southern Idaho is called Thousand Springs for exactly that reason.
Basis: USGS: the Snake River has excavated a canyon into the basalt of the eastern Snake River Plain aquifer, which discharges from the canyon wall as springs of varying size; Thousand Springs is one of the major spring groups.
Water that has been underground comes out cold and steady. A creek warms up in summer and chills in winter, but spring water arrives at close to the same temperature all year, because the rock above it flattens out the seasons.
Basis: Hydrology: groundwater stays near the average yearly air temperature of the area, so spring discharge changes far less between seasons than surface water does.
Idaho sits at the top of America's table for two foods that could hardly be less alike: potatoes and food-size trout.
Basis: Both are checked against the official USDA tables behind the quizzes on this site (see the potato and trout quizzes below).
Is the same lava plain behind both? Potatoes grow in the plain's volcanic soil, and cold spring water is exactly what a trout farm wants — so it makes a tidy story. But “one rock made both champions” is an explanation people tell, not something the tables can prove.
How long does a raindrop take to travel through the rock before it reaches the canyon wall? Scientists estimate underground travel times with tracers and measurements, and the answer differs from one part of the plain to another — so treat any single number you hear as a rough one.
※ A hypothesis is an idea that isn't proven yet.
📊 Sources for the rankings mentioned in this note (links to the original data and retrieval dates) are on each quiz page below.