Four months into the expedition this newly discovered species was noted.
Cpt. Clark, September 17, 1804--Colter Killed a Goat like the one I killed and a curious kind of Deer of a Dark gray Colr. more so than common, hair long & fine, the ears large & long, a Small reseptical under the eyes; like and Elk, the Taile about the length of the Common Deer, round (like a Cow) a tuft of black hair about the end, this speces of Deer jumps like a goat or Sheep.
8 fallow Deer 5 Common & 3 Buffalow killed to day. Capt. Lewis saw a hare & killed a Rattle snake in a village of B.[arking] Squarels the wind from S.W. Dryed our provisions, Some of which was much Damaged.
Clark's next description of mule deer is penned the following year when he is on the coast of the Pacific Ocean. The entire entry is given for its rich depiction of natural history.
Capt. Clark, November 19, 1805
Cape Disapointment at the Enterance of the Columbia River into the Great South Sea or Pacific Ocean.
I arose early this morning from under a Wet blanket caused by a Shower of rain which fell in the latter part of the last night, and Sent two men on a head with directions to proceed on near the Sea Coast and Kill Something for brackfast and that I should follow my self in about half an hour. after drying our blankets a little I set out with a view to proceed near the Coast the direction of which induced me to conclude that at the distance of 8 or 10 miles, the Bay was at no great distance across. I overtook the hunters at about 3 miles, they had killed a Small Deer on which we brackfast[ed], it Comen[c]ed raining and continud moderately untill 11 oClock AM.
after takeing a Suptious brackfast of Venison which was rosted on Stiks exposed to the fire, I proceeded on through ruged Country of high hills and Steep hollers on a course from the Cape N 20[degrees] W. 5 miles on a Direct line to the commencement of a Sandy coast which extended N. 10[degrees] W. from the top of the hill above the Sand Shore to a Point of high land distant near 20 miles. this point I have taken the Libert of Calling after my particular friend Lewis. at the commencement of this Sand beech the high lands leave the Sea Coast in a Direction to Chinnook river, and does not touch the Sea Coast again below point Lewis leaveing a low pondey Countrey, maney places open with small ponds in which there is great numbr. of fowl I am informed that the Chinnook Nation inhabit this low countrey and live in large wood houses on a river which passes through this bottom Parrilal to the Sea coast and falls into the Bay.
I proceeded on the sandy coast 4 miles, and marked my name on a Small pine, the Day of the month & year, &c. and returned to the foot of the hill, from which place I intended to Strike across to the Bay, I saw a Sturgeon which had been thrown on Shore and left by the tide 10 feet in length, and Several joints of the back bone of a Whale, which must have foundered on this part of the Coast. after Dineing on the remains of our Small Deer I proceeded through over a land SE with Some Ponds to the bay distance about 2 miles, thence up to the mouth of Chinnook river 2 miles, crossed this little river in the Canoe we left at its mouth and Encamped on the upper side in an open sandy bottom. The hills next to the bay [on] Cape disapointment to a Short distance up the Chnnook river is not verry high thickly Coverd. with different Species of pine &c. maney of which are large, I observed in maney places pine of 3 or 4 feet through growing on the bodies of large trees which had fallen down, and covered with moss and yet part Sound. The Deer of this Coast differ materially from our Common deer in as muech as they are much darker, deeper bodied, Shorter ledged horns equally branched from the beem the top of the tail black from the rute to the end. Eyes larger and do not lope but jump.