Question: Which state was populated by the expanse of the Oregon Trail, which can also be found in the Palouse region of the United States?

Context paragraphs:
Salt Lake Cutoff: The Salt Lake Cutoff is one of the many shortcuts (or cutoffs) that branched from the California, Mormon and Oregon Trails in the United States.  It led northwest out of Salt Lake City, Utah and north of the Great Salt Lake for about 180 mi before rejoining the California trail near the City of Rocks, Idaho.  From there Oregon Trail travelers could easily travel down the Raft River valley portion of the California Trail to return to the Oregon Trail.  It provided a way to stop in Salt Lake City (the only significant city on the trail then) for repairs, fresh supplies, fresh livestock etc..  In later years it was used by tens of thousands of pioneers and miners going east and west on their way to or from the future states of California, Oregon, Utah, Idaho, Montana, Nevada or Washington.

U.S. Route 195: U.S. Route 195 (US 195) is a north–south United States Highway, of which all but 0.65 miles of its 94.42 miles (1.05 of 151.95 km) are within the state of Washington.  The highway starts in rural Idaho north of the city of Lewiston as a state highway in an interchange with US 95.  As the road crosses into Washington it becomes a state highway that connects communities in the Palouse region of Eastern Washington.  US 195 travels north, serving the cities of Pullman, Colfax and Rosalia in Whitman County before continuing into Spokane County to its terminus in the city of Spokane at an interchange with Interstate 90 (I-90).

Goodale's Cutoff: Goodale's Cutoff formed a spur of the Oregon Trail beginning in Idaho, United States.  The cutoff left the trail near Fort Hall, crossed the Snake River Plain to the Lost River, and then turned west to the area of Boise, crossing Camas Prairie.  It rejoined the main trail from Ditto Creek to Boise, then ran to the north of the main trail, crossing the Snake River into Oregon at Brownlee's Ferry.  In Oregon travelers could now reach the Eagle Valley and Pine Valley areas, and the gold mines in Auburn.  The cutoff rejoined the main Oregon Trail at the Powder River, near Baker City.

Coryell Pass: Coryell Pass is a gap located near Eugene in Lane County, Oregon, United States, near the confluence of the Coast Fork and Middle Fork of the Willamette River.  The gap is formed by the river between Eugene's South Hills and Springfield's Quarry Butte.  The pass is commemorated by a brass marker located on Franklin Boulevard, on what was formerly the route of Pacific Highway.  The marker, which was placed by the Daughters of the American Revolution (D.A.R.), reads "Coryell Pass, Oregon Trail, 1846, Erected by Oregon Lewis and Clark Chapter D.A.R., 1917".  The pass was on the southern route of the Oregon Trail blazed by Jesse Applegate and known as the Applegate Trail.

Giant Palouse earthworm: The giant Palouse earthworm or Washington giant earthworm ("Driloleirus americanus", meaning "lily-like worm") is a species of earthworm belonging to the genus "Driloleirus" found in the Palouse region of Eastern Washington State as well as parts of Idaho in the United States.  The worm was discovered in 1897 by Frank Smith near Pullman, Washington.  It can burrow to a depth of 15 ft .

McCroskey State Park: McCroskey State Park (full name: Mary Minerva McCroskey State Park) is a state park in the northwest United States, located in northern Idaho in the Palouse region.  At 5300 acre , this wilderness area is Idaho's second-largest state park.  It stretches along a ridge in Latah and Benewah Counties, along the border with Washington.

Oregon Trail, Wells Springs Segment: The Oregon Trail, Wells Springs Segment, also known as the Oregon Trail, Boardman Bombing Range Segment, is part of an historic east–west migration route crossing Morrow County in the U.S. state of Oregon.  About 250,000 emigrants from the United States used the trail between 1841 and 1846 to travel between the U.S. state of Missouri and the Willamette Valley in western Oregon.

Oregon Trail: The Oregon Trail is a 2170 mi historic east–west, large-wheeled wagon route and emigrant trail in the United States that connected the Missouri River to valleys in Oregon.  The eastern part of the Oregon Trail spanned part of the future state of Kansas, and nearly all of what are now the states of Nebraska and Wyoming.  The western half of the trail spanned most of the future states of Idaho and Oregon.

Palouse: The Palouse ( ) is a region of the northwestern United States, encompassing parts of southeastern Washington, north central Idaho and, by some definitions, parts of northeast Oregon.  It is a major agricultural area, primarily producing wheat and legumes. Situated about 160 mi north of the Oregon Trail, the region experienced rapid growth in the late 19th century and was once Washington's most populous region, surpassing even the Puget Sound area.

Washington State University: Washington State University (WSU) is a public research university in Pullman, Washington, in the Palouse region of the northwest United States.

Supporting paragraphs: Palouse Oregon Trail
Answer: Washington