Question: A large tributary of the Clearwater River flows within a forest with how many acres?

full_context: Document 1: Clearwater River (British Columbia): The Clearwater River is the largest tributary of the North Thompson River, joining it at the community of Clearwater, British Columbia. The Clearwater rises from glaciers in the Cariboo Mountains and flows in a mostly southerly direction for 201 km to the North Thompson. Its entire course, except the last 5 km , is within Wells Gray Provincial Park. Its confluence with the North Thompson is protected by North Thompson River Provincial Park.
Document 2: Snake River: The Snake River is a major river of the greater Pacific Northwest in the United States. At 1078 mi long, it is the largest tributary of the Columbia River, the largest North American river that empties into the Pacific Ocean. Rising in western Wyoming, the river flows through the Snake River Plain of southern Idaho, then through the rugged Hells Canyon area via northeastern Oregon and the rolling Palouse Hills, to reach its mouth near the Washington Tri-Cities area, where it enters the Columbia. Its drainage basin encompasses parts of six U.S. states, and its average discharge is over 54000 cuft/s .
Document 3: Middle Fork Clearwater River: The Middle Fork Clearwater River is a short, but high volume river in northern Idaho and is the major source of the Clearwater River, a tributary of the Snake River. The Middle Fork flows west for 23 mi from the confluence of the Selway River and Lochsa River at Lowell, to the town of Kooskia where it joins with the South Fork Clearwater River to create the Clearwater River. The Middle Fork's entire length is within Idaho County, although a small portion of its watershed extends into Clearwater County.
Document 4: Selway River: The Selway River is a large tributary of the Middle Fork of the Clearwater River in the U.S. state of Idaho. It flows within the Selway-Bitterroot Wilderness, the Bitterroot National Forest, and the Nez Perce National Forest of North Central Idaho. The entire length of the Selway was included by the United States Congress in 1968 as part of the National Wild and Scenic Rivers Act.
Document 5: Imnaha River: The Imnaha River is a 73.3 mi tributary of the Snake River in the U.S. state of Oregon. Flowing generally east near the headwaters and then north through Wallowa County, the entire river is designated Wild and Scenic. It follows a geologic fault to the Snake River, and in addition to land in the Wallowa–Whitman National Forest and private land, its corridor includes parts of three special management areas: the Eagle Cap Wilderness, Hells Canyon National Recreation Area, and Hells Canyon Scenic Byway. The Imnaha flows by the unincorporated community of Imnaha, the only settlement along its course, and enters the Snake River roughly 4 mi from the larger river's confluence with the Salmon River of Idaho and 192 mi from its confluence with the Columbia River.
Document 6: Custer National Forest: Custer National Forest is located primarily in the south central part of the U.S. state of Montana but also has separate sections in northwestern South Dakota. With a total area of 1188130 acre , the forest comprises over 10 separate sections. While in the westernmost sections, Custer National Forest is a part of the Greater Yellowstone Ecosystem, the easternmost sections are a combination of forest "islands" and grasslands. A portion of the forest is also part of the Absaroka-Beartooth Wilderness and constitutes over a third of the wilderness land. South of Red Lodge, Montana, the Beartooth Highway (U.S. 212) passes through the forest en route to Yellowstone National Park.
Document 7: Beartooth Mountains: The Beartooth Mountains are located in south central Montana and northwest Wyoming, U.S. and are part of the 900,000 acre (3,600 km) Absaroka-Beartooth Wilderness, within Custer, Gallatin and Shoshone National Forests. The Beartooths are the location of Granite Peak, which at 12,807 feet (3,904 m) is the highest point in the state of Montana. The mountains are just northeast of Yellowstone National Park and are part of the Greater Yellowstone Ecosystem. The mountains are traversed by road via the Beartooth Highway (U.S. 212) with the highest elevation at Beartooth Pass (10,947 ft, 3,345 m). The name of the mountain range is attributed to a rugged peak found in the range, Beartooth Peak, that has the appearance of a bear's tooth.
Document 8: Selway-Bitterroot Wilderness: The Selway-Bitterroot Wilderness is a protected wilderness area in the states of Idaho and Montana, in the northwestern United States.
Document 9: Clark Fork River: The Clark Fork, or the Clark Fork of the Columbia River, is a river in the U.S. states of Montana and Idaho, approximately 310 mi long. The largest river by volume in Montana, it drains an extensive region of the Rocky Mountains in western Montana and northern Idaho in the watershed of the Columbia River. The river flows northwest through a long valley at the base of the Cabinet Mountains and empties into Lake Pend Oreille in the Idaho Panhandle. The Pend Oreille River in Idaho, Washington, and British Columbia, Canada which drains the lake to the Columbia in Washington, is sometimes included as part of the Clark Fork, giving it a total length of 479 mi , with a drainage area of 25820 sqmi . In its upper 20 mi in Montana near Butte, it is known as Silver Bow Creek. Interstate 90 follows much of the upper course of the river from Butte to northwest of Missoula. The highest point within the river's watershed is Mount Evans at 10641 ft in Deer Lodge County, Montana along the Continental Divide.
Document 10: Bitterroot National Forest: Bitterroot National Forest comprises 1.587 million acres (6,423 km²) in west-central Montana and eastern Idaho, of the United States. It is located primarily in Ravalli County, Montana (70.26% of the forest), but also has acreage in Idaho County, Idaho (29.24%), and Missoula County, Montana (0.49%).
Document 11: Gallatin National Forest: Founded in 1899, Gallatin National Forest is located in south central Montana, United States. The forest comprises 1819515 acres and has portions of both the Absaroka-Beartooth and Lee Metcalf Wilderness areas within its boundaries. Gallatin National Forest borders Yellowstone National Park on the north and northwest and is part of the Greater Yellowstone Ecosystem, a region which encompasses almost 20000000 acres . The forest is named after Albert Gallatin (1761–1849), U.S. Secretary of the Treasury and scholar of Native American languages and cultures.
Document 12: Beaverhead-Deerlodge National Forest: The Beaverhead-Deerlodge National Forest is the largest of the National Forests in Montana, United States. Covering 3.36 e6acre , the forest is broken into nine separate sections and stretches across eight counties in the southwestern area of the state. President Theodore Roosevelt named the two forests in 1908 and they were merged in 1996. Forest headquarters are located in Dillon, Montana. In Roosevelt's original legislation, the Deerlodge National Forest was called the Big Hole Forest Reserve. He created this reserve because the Anaconda Copper Mining Company, based in Butte, Montana, had begun to clearcut the upper Big Hole River watershed. The subsequent erosion, exacerbated by smoke pollution from the Anaconda smelter, was devastating the region. Ranchers and conservationists alike complained to Roosevelt, who made several trips to the area.
Document 13: South Fork Clearwater River: The South Fork Clearwater River is a 62 mi long river in north-central Idaho in the United States. Draining about 1175 mi2 , the South Fork joins with the Middle Fork Clearwater River to form the Clearwater River, a major tributary of the Snake River.
Document 14: Bitterroot Range: The Bitterroot Range is a mountain range and a subrange of the Rocky Mountains that runs along the border of Montana and Idaho in the northwestern United States. The range spans an area of 24223 mi2 and is named after the bitterroot ("Lewisia rediviva"), a small pink flower that is the state flower of Montana.
Document 15: Missoula, Montana: Missoula is a city in the U.S. state of Montana and is the county seat of Missoula County. It is located along the Clark Fork River near its confluences with the Bitterroot and Blackfoot Rivers in western Montana and at the convergence of five mountain ranges, thus is often described as the "hub of five valleys". In 2016 , the United States Census Bureau estimated the city's population at 72,364 and the population of the Missoula Metropolitan Area at 116,130. In the 1990s, Missoula overtook GreatFalls as Montana’s second‑largest city, behind Billings. Missoula is home to the University of Montana, a public research university.
ground_truth: 1.587 million