This is a Fossil of a Leaf from the Eocene period. It was found in Green River, Wyoming. This piece measures approx. 92 x 72 mm: thickness is 4 mm: weight is 63 grams.  Note: this fossil had broken at some point and was repaired. 
 
Leaf Fossil Green River Wyoming are from the Green River Formation of Rocks that cover parts of Utah, Colorado. They formed from mountain lakes during the Eocene epoch about 48 million years ago.