The seven mile American Bottom Baseline is the anchor from which the entire transcontinental triangulation survey west of the Mississippi begins. The baseline was defined by two monuments established in 1872—known to surveyors as American Bottom Upper Base (38° 39' 50.22122" N 90 00' 57.67079" W, 522.00 FASL) and American Bottom Lower Base (38° 36' 16.04689" N 90 03' 03.02680" W, 481.91 FASL)— in the form of two 14-inch-square stones, each set partway up the escarpment. From these points, surveyors began their great triangulation by sighting a standpipe in North St. Louis, a point coarsely named ”Insane Asylum” after the mental hospital in the southwestern portion of the city, and a point named Minoma in North St. Louis County. This last point, one of the first-order anchors to the triangulation of the country, is itself built on the foundation of erasure. The name Minoma was the name given to a local landmark—a 26-story mansion built in 1856 by Jefferson Clark (the son of William Clark of Lewis and Clark fame)—that was demolished in 1960. Similarly, to date only the lower base monument remains—with the upper base lost to road construction and erosion.