E-mail from: jrjpcg@gmail.com identifying the photos:

The identity of the NATURAL FALLS is actually KEOKUK FALLS.  KEOKUK FALLS was a liquor / border town located in the bottom of the NE panhandle corner of Pottawatomie County.

The town was a violent outlaw/saloon town whose hey day was 1891 to 1907.  Statewide prohibition brought about the demise of the town.

The WATER FALLS were located one mile west and a quarter to half mile south of the town on the NORTH CANADIAN RIVER.  

I've been researching KEOKUK FALLS for the last year.  I have obtained an old book titled LOCALIZED HISTORY OF POTTAWATOMIE COUNTY TO 1907 as well as another book titled THE HISTORY OF POTTAWATOMIE COUNTY.  The history of these falls as well as the town is very substantial and significant.  

The town started in 1891 but the history of the falls date back to the 1700's.  It was easy to identify your pictures as KEOKUK FALLS by simply comparing the window locations on the GRIST MILL.  The books contain more pictures of the falls making the comparisons much more obvious.  The link to the picture below should solidify this for you.  In fact, I think in your 1st picture you can make out the letters "KEO" in the blurred wording above NATURAL FALLS.  I was so glad to stumble across your pictures of the falls.  I came across your website as I was looking for information on John Beard, one of the founders of SHAWNEE, who moved to ADA in 1900.  John Beard Interview.

These falls are legendary and people are trying to find them to this date.  I think I have located them via satellite maps and will be making a journey to do some digging.  

Note:

(The falls disappeared when the North Canadian river changed it's course due to floods eroding the banks. The "town" was very active in the early 1920's and 1930's, however it became a ghost town)

For more information: 

Ghost Towns of Oklahoma 
Keokuk Falls - "Ghost" town of Pottawatomie County, Oklahoma
Keokuk Falls - Flickr from Yahoo!