Minnesota - North Dakota - South Dakota Tri-state

Description

The tri-point witness monument shown on the USGS topo map is easy to reach by farm roads near White Rock, SD. With a 4WD vehicle you can get quite close to it. There is some confusion, however, as to the exact location of the tri-point. The monument's E face contains an inscription stating that the tri-point lies 9 chains (594 feet) to the E. This corresponds to a position in the Bois de Sioux River, as shown on the following carefully measured map fragment (The intermediate tick mark corresponds to 594 feet.)

The map shows the tri-point only 80 feet E of the monument. We carefully measured the position of the USGS tri-point using electronic and paper copies of the map to obtained coordinates. We navigated to that position using GPS and found a partially exposed large rock, to which we added several smaller stones to form an embryonic cairn. We paced off a distance of 135 feet from the cairn to the witness monument. The 55 foot discrepancy between the map measurement and the paced distance is just barely within the 18 meter inherent GPS error and close to the 40-foot map accuracy standard used on the topo map, so our cairn is probably between 15 and 95 feet too far E.

Our best guess is that the inscription on the monument is correct (i.e., the tri-point is in the river). Historically, the river was the boundary between Minnesota and the Dakota Territory. We find it remarkable, though, that the tri-point presently is in the river because the river supposedly has been straightened and re-routed since the boundary was established.

Photos (click to enlarge)

	Brian Butler and Gregg Butler at the witness monument on July 26, 2001. Photo by Brian J. Butler
	Brian Butler pointing at the location of the tri-point as depicted on the USGS topo map, 135 feet east of the witness monument. Photo by Gregg A. Butler
	The embryonic cairn. Photo by Brian J. Butler
	The east face of the witness monument indicating the tri-point 9 chains (594 feet) to the east. Photo by Brian J. Butler
	The rarely photographed west face of the witness monument. Photo by Brian J. Butler, 2003
	This photo was taken from the point, which the USGS depicts as the trifinium, 80 feet east of the witness monument. Too bad the large rock in the foreground does not coincide with the trifinium. Photo by Brian J. Butler, 2003
	The water level in the Bois de Sioux was very low when this picture was taken on July 26, 2003, making it possible to reach the point 9 chains east of the witness monument without swimming. The river is 6 to 8 feet wide in this photo. Photo by Brian J. Butler, 2003
	This photo was taken from the dry riverbed at a point approximately 9 chains east of the witness monument. The view is to the west. Photo by Brian J. Butler, 2003