This EarthCache is located in a Nebraska State Historical Park

Park permit required for all vehicles

This is a day use area only, grounds open at 8 a.m.

Closing time varies with the season and is posted near the entrance.

There is no admission fee for the Visitor's Center

While visiting this Earthcache, take the time to explore the reconstructed fort. The first U.S. fort west of the Mississippi, built on this Alluvial Fill Terrace on the recommendation of Lewis and Clark.

The Harold W. Andersen Visitor Center is open daily from Memorial Day weekend through Labor Day from 10 a.m. to 5 p.m. The visitor Center is also open on weekends only from May 5 through May 20 and September 8th through October 21. Park grounds open at 8 a.m. daily.

Parking for the visitor center is located at N 41°27.310 W 096°00.960

Parking for the fort reconstruction is located at N 41°27.130 W 096°00.820

The Journal Entries

Clark July 30 1804

Capt. Lewis and my Self walked in the Prarie on the top of the Bluff and observed the most butifull prospects imagionable, this Prarie is Covered with grass about 10 or 12 Inch high, (Land rich)    rises about ½ a mile back Something higher and is a Plain as fur as Can be Seen, under those high Lands next the river is butifull Bottom interspersed with Groves of timber, the River may be Seen for a great Distance both above & below meandering thro: the plains between two ranges of High land which appear to be from 4 to 20 ms. apart,

Ordway July 30 1804

we proceded on past a high bank & bottom prarie.    arived at high blufs on S. S.    we camped about 7 oClock close under the foot of the bluffs in a Strip of woods which make along under the Ridge to the River    the Timber is coffee nut white oak Black walnut Elm bass wood or lynn hickery &C-    below this handsome bottom prarie, above the Timber and bluffs is a beautiful high prarie, I think it is the Smothest, & prittyset place for a Town I ever Saw.    back of this high Large prarie, their is uneven praris Some Timber in the vallies & on the branches &C-

Clark Aug 3 1804

The Situation of this place which we Call Council Bluff which is handsom ellevated    a Spot well Calculated for a Tradeing establishment,   the Bank high & leavel on top well Calculated for a fort to Command the Countrey and river    the low bottom above high water & well Situated under the Command of the Hill for Houses to trade with the Natives    a butifull Plain both abov and below    at no other bend on either Side does the High land touch the river for Some distance up, as I am told.

The Geology

N 41° 27.142 W 096° 00.674

Formation of Floodplains and Fill Terraces

   Ancient floodplains are represented in the landscape by stream or fill terraces that remain relatively high above present floodplains. Both ancient and present flood plains are created when the gradient becomes slight and the decreasing velocity deposits sediments  from higher regions. Under these conditions a stream will often meander and widen the valley by eroding  the outside curve of the stream loops due to a higher velocity current and depositing on the inside curves where the velocity is lower. This tends to level out the stream valley. In times of flood, the rush of water both erodes, when the velocity is high, and deposits when receding, resulting in further planation (creation of flat terrain) of the stream's valley.

     Fill terraces begin when an existing valley or floodplain is filled with alluvium (sediments transported and deposited by flowing water.) The valley may fill due to an increased bedload from glaciation or a change in the carrying capacity of the stream which would cause the stream to deposit instead of transport material. The fill terrace is created when conditions change and the stream begins to downcut into the alluvial material, leaving benches above the present stream channel. These cycles can be repeated several times in some areas resulting in what is known as "nested terraces."

EarthCache Logging requirements:

Post an optional photo of yourself, an avatar, or your gps at your favorite part of the Fort, visitor center or grounds.

And

In an email to the cache owner:

Estimate the height from the deck at the Council Bluff, N 41° 27.142 W 096° 00.674 to the floodplain below. Give the name of the feature visible below the deck on the floodplain. Also describe the view to the east beyond the bluff and the view to the west beyond the fort and state why these features point to this being an alluvial fill terrace.

You will not need to wait for a response to log the cache online, however, logs not meeting all of the requirements within a reasonable time frame will be deleted.

Attention Benchmark Hunters!

There is a National Geodetic Survey Commemorative Monument at N 41° 27.201 W 096° 00.559 between the visitor center and the life size, bronze statues of the First Tribal Council

One of a series of commemorative Lewis and Clark survey monuments

To make the most of your visit, there are Living History demonstrations several weekends each summer, for details and dates, please visit: The Friends of Fort Atkinson

References:

Wikipedia contributors, "Stream terrace," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Stream_terrace&oldid=220201304 (accessed June 20, 2008).

Wikipedia contributors, "Floodplain," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Floodplain&oldid=220387910 (accessed June 20, 2008).

University of Nebraska Press / University of Nebraska-Lincoln Libraries-Electronic Text Center. The Journals of the Lewis and ClarkExpedition. http://lewisandclarkjournals.unl.edu.

Lewis and Clark and the Geology of Nebraska and Parts of Adjacent States          Educational Circular No. 18. December 2003.Published by Conservation and Survey Division/School of Natural Resources, Institute of Agriculture and Natural Resources/College of Arts and Sciences, University of Nebraska-Lincoln. Copyright (c) 2003 Robert F. Diffendal & Anne P. Diffendal.

http://digitalcommons.unl.edu/natrespapers/76/