Here’s a cool map taken from the archives of the Minnesota Ground Water Association (yes, that’s a thing), compiled by underground researcher Greg Brick (author of the eye-opening Subterranean Twin Cities). Here Brick has mapped out all the springs of along the Minnesota and Mississippi rivers in the core Twin Cities area.

Check it out:

In the article, which you can find online, Brick describes his rather adventurous process:

My first attempt at mapping, in January 1993, lasted all of the day. I had framed the plan of locating the springs in wintertime. Springwater freezes to form icicles on the bluffs…

The close-up approach proved fatiguing — and dangerous.

I spent more time mountaineering than mapping. I had to walk along the top of a wedge of loose stones that mantled the foot of the bluffs. This material, at the angle of repose, was concealed by snow. I had some nasty falls … and nearly ended up with frostbite. At the end of the day, as the sun saw setting, I remember going down on my belly and slithering behind an icicle as stout as an oak tree, to get the next foothold.

Pretty cool! This time of year, it’s fun to think of spring.