The James River is a tributary of the Missouri River. It is about
710 miles long in the states of North Dakota and South Dakota. The
river and the river’s valley were formed by the James Lobe of
the most recent ice age glaciers. A glacier lobe is a tongue-like
projection from a continental glacier's main mass. They are called
lobes because they have an earlobe type of shape. The southern edge
of the James Lobe is the northern side of the modern Missouri River
valley in the area of Yankton, South Dakota.
The James River valley usually is 50 to 75 miles wide. The
valley narrows considerably in the southernmost regions. The
coordinates of this EarthCache are at one of the narrowest parts of
the James River valley, and thus one of the narrowest parts of the
James Lobe of the Wisconsin glacier. When you visit the area please
notice the hills and rocks. Look for rocky hills.
Surface rocks in the James River valley tell a story of
glaciations. Glaciers eroded and deposited rocks as they advanced
and as they retreated. Glacial moraines were formed when glaciers
melted and retreated. These moraines appear to be mounds of a
mixture of rock, gravel, and boulders. Terminal or end moraines
were formed at the terminal end of a glacier. Lateral moraines were
formed on the sides of the glacier. Farmers in South Dakota and
elsewhere have for years battled the rounded rocks of glaciated
farm land.
In addition to leaving behind those piles of rocks and boulders
(moraines) the melting waters formed a large lake that covered much
of the James River valley area. The water eventually drained away.
The slow meandering James River is all that remains of that great
lake.
Your goal for this EarthCache is to observe the land features,
make measurements, and draw some conclusions.
The observations and measurements can be done from the roadside
of a Yankton County road called 303rd Street. As a public roadway
no landowner permissions are required. Please do not attempt to
take elevation measurements from the river; measure from the bridge
instead.
Information to email:
1/ Elevation at the high point of the hills east of the
river.
2/ Elevation at the high point of the hills west of the
river.
3/ Distance from east high point to west high point
4/ Elevation of river at bridge (OK to take from bridge and
subtract 20 feet).
5/ Conclusions. Based on your measurements how deep could that
James River/Lake have been at that location after the glacier
melted? How wide could it have been?
6/ Observation. Do the hills east and west of the James River
appear to be moraines? You may skip this part if snow covering
prevents you from seeing the ground.
Information to include in log (recommended but not
required).
1/ A photograph that shows you were there – or shows
something scenic of the area.
2/ Your impressions of the geology of the area. Please do not
reveal any of the required information though.
Go ahead and log your visit. I probably will not respond to your
email unless your information is incomplete or inaccurate.
Sources of information:
“Nature and timing of the latest Wisconsin advance of the
James River lobe, South Dakota” from American Geophysical
Union, Fall Meeting 2009, abstract #PP21A-1332
“James River (Dakotas)” Wikipedia, the free
encyclopedia (accessed March 2010)
“James River Valley – Glaciers”
http://at008.k12.sd.us/james_river_valley_glaciers.htm
Roadside Geology of South Dakota by John Paul Gries