The travelers kept meticulous journals, writing the first accounts of 122 animals and 178 trees and plants. In doing so they left us an invaluable record of what America looks like 200 years ago, with its "immence herds of Bufaloe, Elk, deer, and Antelope fee[d]ing in one common and boundless pasture."

"[O]n the Mountains great number of goat and a kind of anamale with circular horns, this animale is nearly the size of a Small Elk." The Audubon bighorn sheep, the subspecies first observed by Clark along the upper Missouri River, has since gone extinct.

Bighorn sheep were reduced to a fraction of their original number because of unregulated hunting and disease carried by domestic sheep. Recently, historic ranges have been repopulated by sheep from healthy herds.

"It is now the season at which the buffaloe begin to coppelate and the bulls keep up a tremendous roaring--we could hear them for many miles and there are such numbers of them that there is one continuous roar."

At the time of Lewis and Clark, there may have been up to 60 million bison, but by the turn of the 20th century, only a few hundred remained. Today their numbers have grown to some 300,000, mostly in private herds.

"Capt. Clark & Drewyer killed the largest brown bear this evening which we have yet seen. It was a most tremendous looking animal . . . . He measured 8 ft. 7 1/2 in. from nose to extremity of hind feet."

Two hundred years ago, as many as 100,000 grizzlies roamed the West. Today barely 1,000 remain in remote areas of Idaho, Montana, and Wyoming. Sierra Club is working to keep grizzly bears protected in the Greater Yellowstone Ecosystem.

"[T]he Village of those animals Covered about 4 acres of Ground on a gradual descent of a hil and Contains great numbers of holes on the top of which those little animals Set erect, make a Whistling noise and whin allarmed."

Prairie dogs used to number 5 billion, and their enormous villages supported scores of other creatures. Remnant populations are still key to the survival of endangered species like the black-footed ferret, ferruginous hawk, and swift fox. Eleven states are now working to double prairie-dog conservation areas by 2011.