Question: The Snake River is a  tributary of which river on which Richland stands?
Context: Middle Fork Little Snake River is a 17.5 mi tributary of the Little Snake River in Routt County, Colorado.  It flows from a source near the Continental Divide in Routt National Forest to a confluence with the North Fork Little Snake River that forms the Little Snake River. Richland is a city in Benton County in the southeastern part of the State of Washington, at the confluence of the Yakima and the Columbia Rivers.  As of the 2010 census, the city's population was 48,058.  April 1, 2013, estimates from the Washington State Office of Financial Management put the city's population at 51,150.  Along with the nearby cities of Pasco and Kennewick, Richland is one of the Tri-Cities, Washington, and is home to the Hanford nuclear site. 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. The Snake River Range is located in the U.S. states of Wyoming and Idaho and includes 10 mountains over 9000 ft .  The tallest peak in the range is Mount Baird at 10025 ft .  The range trends northwest to southeast and is bordered on the north by the Teton Range and the two ranges meet at Teton Pass.  The Snake River Range is bordered by the Palisades Reservoir to the west and the Snake River, which sweeps completely around the eastern, southern and western part of the range.  The range is approximate 30 mi north to south and 33 mi west to east, covering 528 sqmi .  Along the southern boundary, the Snake River passes through Grand Canyon, also known as the Snake River Canyon.  U.S. Route 26/U.S. Route 89 follows the course of the Snake River from Hoback Junction to the Palisades Reservoir. The Hoback River, also called the Fall River , is an approximately 55 mi -long tributary of the Snake River in the U.S. state of Wyoming.  It rises in the northern Wyoming Range of Wyoming and flows northeast through the Bridger-Teton National Forest, before turning northwest to join the Snake just downstream of Jackson Hole, near the head of the Snake River Canyon and near the town of Hoback.  The largest tributary of the Hoback River is its South Fork, which joins it near the town of Bondurant, where the river spreads onto a large marshy flat in a braided floodplain once known as Jackson's Little Hole., but now referred to as the "Hoback Basin".  However, most of the river flows through narrow valleys and in its lower course, steep mountain canyons.  The entire length of the Hoback is free flowing and unobstructed by dams.  About 30 mi downstream from the confluence with the Hoback River, the Snake River crosses into the state of Idaho and is impounded by Palisades Dam. North Fork Little Snake River is a 13.1 mi tributary of the Little Snake River in Colorado and Wyoming.  It flows from a source in the Medicine Bow National Forest of Carbon County, Wyoming to a confluence with the Middle Fork Little Snake River in Routt County, Colorado that forms the Little Snake River. The Snake River Aquifer is a large reservoir of groundwater underlying the Snake River Plain in the southern part of the U.S. state of Idaho.  Most of the water in the aquifer comes from rain and melting snow that flows onto the plain from the Snake River, Big Lost River, Bruneau River, and other watercourses of southern Idaho.  Measuring about 400 mi from east to west, it is an important water source for agricultural irrigation in the Plain.  The Snake River Aquifer is commonly defined as two separate parts, separated by Salmon Falls Creek.  These are the Eastern Snake River Plain Aquifer and Western Snake River Plain Aquifer. The Gros Ventre River ("pronounced GROW-VAUNT") is a 74.6 mi tributary of the Snake River in the state of Wyoming, USA.  During its short course, the river flows to the east, north, west, then southwest.  It rises in the Gros Ventre Wilderness in western Wyoming, and joins the Snake River in the Jackson Hole valley.  In 1925, the massive Gros Ventre landslide dammed the river and formed Lower Slide Lake.  The natural dam collapsed in 1927, flooding the downstream town of Kelly, Wyoming.  The river is noted for the excellent trout fishing along its length, where native Snake River Fine-spotted Cutthroat Trout average 12 to , with some to 20 in . The Columbia River is the largest river in the Pacific Northwest region of North America.  The river rises in the Rocky Mountains of British Columbia, Canada.  It flows northwest and then south into the US state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean.  The river is 1243 mi long, and its largest tributary is the Snake River.  Its drainage basin is roughly the size of France and extends into seven US states and a Canadian province.  The fourth-largest river in the United States by volume, the Columbia has the greatest flow of any North American river entering the Pacific. The Greys River is a tributary of the Snake River, flowing through western Wyoming in the United States.  The river is about 62 mi long, starting high up in the Wyoming Range, 45 mi south of the town of Alpine in Lincoln County.  The river eventually flows into the Snake River in the Snake River Canyon, joining it just east of Alpine.  The Greys River is generally a rushing mountain stream that separates the high Wyoming Range (east) from the Salt River Range (west).  It joins the Snake River just above the intersection of U.S. highways 89 and 26.  Just a short distance downriver from the confluence of the two rivers, the Snake widens quickly and passes through Alpine and enters the Palisades Reservoir.  The largest tributary of the Greys River is the Little Greys River.
Answer: Columbia River