This excursion is mostly confined to Montana Highway 80, a well maintained paved road.  Begin at Fort Benton, at the west end of the highway bridge over the Missouri.  Remain on Highway 80 for 32.5 miles. Just before arriving at the town of Square Butte there is a spectacular view to the west [Site 4] of a valley with high rock walls.  Only an immense river could have cut this valley, but there is only an insignificant stream there now.  Leading off to the the west there is an unimproved country road which takes us to the base of the cliff on the north side of the Sag.  This cliff is solid rock, and exposes the side of a laccolith that was eroded by the Sag.  The dark rock is shonkinite, which has been intruded between layers of sandstone and other rocks to form a broad, relatively flat laccolith.

See detail map

After viewing the cliff retrace the route back to the bridge that crosses the minor stream of Flat Creek.  Notice that the stream follows a valley that leads away from the Sag toward the North.  While the principal route of the stream flow during the ice age was probably along Arrow Creek to the south, the rivers could have followed this broad valley which also presents a potential outlet for the Shonkin Sag.

Return to the town of Geraldine and take a local road leading directly west for about 8.4 miles, where there is an overlook with impressive views of the Sag and Square Butte in the distance [Site 5].  Both here and near Square Butte it is apparent that the valley that constitutes the Shonkin Sag is immense, and must have been excavated by torrents of water working for a very long time.  It is only slightly smaller than the Ice Age overflow channels of the Columbia River, such as the Grand Coullee.

The return route again follows Highway 80 back to Fort Benton.  About 5 miles before arriving at the town there is an imposing view looking over the broad pre-glacial Missouri Valley.  The valley walls have been much eroded and smoothed by glaciers, so it takes a bit of imagination to see them.  Just imagine that the deep present-day Missouri channel is not there, and you can visualize a broad trough running in a southwest to northeast direction.

Loop route, with total distances:

Waypoint	mi	km	Lat	Long
Start, Fort Benton, Highway 80	0.00	0.00	N47° 48.97'	W110° 40.14'
Town of Square Butte, View of Shonkin Sag	32.5	52.3	N47° 39.52'	W110° 12.13'
View of Cliff	37.3	66.7	N47° 32.56'	W110° 17.09'
Retrace route to Flat Creek	44.4	71.4	N47° 33.52'	W110° 12.96'
Geraldine (left turn)	45.5	73.2	N47° 36.34'	W110° 15.89'
View of Sag	56.9	91.5	N47° 34.72'	W110° 24.65'
Retrace route to view point	86.3	138.9	N47° 47.91'	W110° 35.10'
Return to Fort Benton	91.3	146.9	N47° 48.97'	W110° 40.14'