Question: What animal did Lewis and Clark newly discover during their 1804 expedition up Old Baldy in Nebraska?

Context paragraphs:
Bald Head Light: Bald Head Lighthouse, known as Old Baldy, is the oldest lighthouse still standing in North Carolina.  It is the second of three lighthouses that have been built on Bald Head Island since the 18th century to help guide ships past the dangerous shoals at the mouth of the Cape Fear river.

Baldy Mountain (Colfax County, New Mexico): Baldy Mountain (official name), Baldy Peak, Mount Baldy, or Old Baldy is the highest peak in the Cimarron Range, a subrange of the Sangre de Cristo Mountains of New Mexico.  It is located in Colfax County, about 6 mi northeast of Eagle Nest.  It rises abruptly, with 3,640 ft of vertical relief (in 3 miles/4.8 km), from the Moreno Valley to the west and has a total elevation of 12441 ft .

Old Baldy (Lynch, Nebraska): Old Baldy, also known as the Tower, is a hill located near the village of Lynch, in Boyd County, in the northern part of the state of Nebraska in the Midwestern United States.  It was visited by the Lewis and Clark Expedition on their way up the Missouri River in 1804; nearby, they discovered a colony of prairie dogs, an animal previously unknown to scientists.

Lewis and Clark Pass (Montana): Lewis and Clark Pass, el.  6424 ft is a mountain pass on the continental divide in Montana.  It lies at the head of the drainages of the west flowing Blackfoot River and the east flowing Dearborn River.  The pass is in the Helena National Forest in Lewis and Clark County.  The Continental Divide Trail traverses north and south through the pass.  At the time of the Lewis and Clark Expedition the pass was a much-used pathway where the native people living in what today is Montana crossed over the continental divide.  The pass was crossed by Meriwether Lewis on July 7, 1806, on the return leg of the Lewis and Clark Expedition with a party of nine men and his dog Seaman.  The pass was named for the expedition's two leaders–Lewis and William Clark.  Lewis and Clark Pass is the only roadless pass on the entire Lewis and Clark National Historic Trail.  It has gone from being one of the most used continental divide passes prior to the pioneer era to one of the least visited passes today.  It can be accessed by a 1.5 mi trail.  Visitors will encounter the pass much as Lewis did in 1806.  The furrows left by the countless dog and horse travois that crossed the pass are still visible (though fading) and this is one of the places along the expedition's route that visitors may still encounter a grizzly bear.  On a clear day, like Meriwether Lewis in 1806 one can see Square Butte in Cascade County, Montana, 40 mi to the northeast.

Mount Harwood: Mount Harwood is the first summit east of Mount San Antonio.  The United States Geological Survey recognized the name to honor California educator and conservationist Aurelia Squire Harwood in 1965.  Prior to this, the peak now known as Thunder Mountain was also referred to as Mount Harwood.  Mount Harwood is located on the East side of the San Gabriel Mountains in the Angeles National Forest near the San Bernardino-Los Angeles county border.  In this area of the San Gabriel Mountains the peaks are the highest.  Because of the elevation Mount Harwood turns out to be ranked the 4th highest peak in the San Gabriel mountains after Dawson Peak, Mount San Antonio or "Old Baldy" being the highest at 10,064 feet (3,068 m).  The only way for hikers or tourists to access Mount Harwood is to take Mt. Baldy Road off I-210.  A National Forest Adventure pass/ National Park access pass must be displayed on a vehicle to access Mount Harwood.

Old Baldy Council: The Old Baldy Council (#043) was founded in 1917 as the Pomona Council.  It changed its name in 1921 to Old Baldy.  The Old Baldy name is from Mount San Antonio, often called "Old Baldy" or "Mount Baldy", the highest peak in the San Gabriel Mountains.

Battle of Old Baldy: The Battle of Old Baldy refers to a series of five engagements for Hill 266 in west-central Korea.  They occurred over a period of 10 months in 1952–1953, though there was also vicious fighting both before and after these engagements.

Black-tailed prairie dog: The black-tailed prairie dog ("Cynomys ludovicianus"), is a rodent of the family Sciuridae found in the Great Plains of North America from about the United States-Canada border to the USA-Mexico border.  Unlike some other prairie dogs, these animals do not truly hibernate.  The black-tailed prairie dog can be seen above ground in midwinter.  A black-tailed prairie dog town in Texas was reported to cover 64000 km2 and included 400,000,000 individuals.  Prior to habitat destruction, this species may have been the most abundant prairie dog in central North America.  This species was one of two described by the Lewis and Clark Expedition in the journals and diaries of their expedition.

Garnet Range: The Garnet Range, highest point Old Baldy Mountain, elevation 7511 ft , is a mountain range northeast of Drummond, Montana in Powell County, Montana.

Beaver Valley (Ontario): The Beaver Valley is a valley in southern Ontario, Canada, at the southern tip of Georgian Bay.  The Beaver River flows north through the valley, emptying into Georgian Bay in the town of Thornbury.  It is a productive agricultural area, producing a significant portion of Canada's apple crop.  It also contains one of Ontario's best-preserved hardwood swamp ecosystems.  The Bruce Trail follows the perimeter of the valley passing several natural landmarks including Old Baldy, the Duncan Crevice Caves, and Eugenia Falls.  The main towns in the valley are Flesherton at the south end, Kimberley, and Thornbury.

Supporting paragraphs: Old Baldy (Lynch, Nebraska) Black-tailed prairie dog
Answer: black-tailed prairie dog