A three kilometer reach of the Mississippi River gorge near downtown St. Paul, Minnesota, is known locally as “Mushroom Valley” because of the abundance of man-made mushroom caves in the sandstone bluffs. Mushroom growing lasted a century, from its introduction by Parisian immigrants in the 1880s until the last cave ceased production in the 1980s during the creation of Lilydale Regional Park. Notable examples are Altendorfer, Bisciglia, Lehmann, and Peltier caves.
Some of the approximately fifty caves originated as sand mines, and not all were used for mushroom growing. Examination of city directories and Sanborn insurance atlases revealed that other common uses were aging of cheese (Land O’ Lakes), lagering of beer (Yoerg’s Brewery), and storage (Villaume Box & Lumber). The University of Minnesota rented caves in the 1930s for experimental ripening of blue cheese. A cave used by the St. Paul Brick Company later was gated as a bat hibernaculum by the Minnesota Department of Natural Resources. Mystic Caverns and Castle Royal were underground nightclubs in the 1930s, the latter hosting the Howdy Party for the 1980 National Speleological Society Convention.
The caves were surveyed during a civil defense study in the early 1960s. The typical cave is a straight, horizontal passage fifty meters long, but often connected by cross-cuts to similar caves on either side, creating network mazes with multiple entrances. A cave operated by the Becker Sand & Mushroom Company is the largest of all, with ten-meter ceilings and more than a kilometer of passages.
Excerpted from SUBTERRANEAN TWIN CITIES.