Located 15 miles from Big Sandy Station and 15 miles from Green River Station probably on north bank of Big Sandy Creek.

http://www.expeditionutah.com/featured-trails/pony-express-trail/wyoming-pony-express-stations/ 

Bishop and Henderson, as well as the U.S. mail contract of 1861, list Big Timber as a station between Big Sandy Creek and Green River. Gregory Franzwa places this station just east of the Slate Creek Cutoff to the Sublette Cutoff, but he does not specifically identify Big Timber Station as a Pony Express site.  Little more is known about this station.

http://www.nps.gov/parkhistory/online_books/poex/hrs/hrs6a.htm#86