The volcano's last eruptions took place from spatter cones about 1,350 years ago, generating basaltic andesite lava deposits.

With an elevation of 7,795 feet (2,376 m) above sea level,[1][2] Mount Washington is located in Deschutes and Linn counties in the U.S. state of Oregon.

[12] The volcano forms a crest of steep, icy mountains with North Cinder Peak and Three Fingered Jack to the south of Mount Jefferson.

[20] Used mostly by hunters, hikers, and climbers,[19] the Mount Washington area includes the Dee Wright Observatory, smaller volcanoes, and parts of the Pacific Crest Trail,[9] which runs north–south through the wilderness[9] for about 16.6 miles (26.7 km).

[9] The area contains large amounts of cinder – more than 200,000,000 cubic yards (0.15 km3)[21][22] – but there are alternate sources in the region, which are sufficient to meet local demands.

[25] The Belknap Hot Spring lies 4 miles (6.4 km) to the southwest of the wilderness area, ejecting water at a rate of 75 U.S. gallons (280 L) per minute with a temperature of 180 °F (82 °C).

On August 26, 1923,[27] Mount Washington was climbed for the first time by six boys from Bend:[7] Ervin McNeal, Phil Philbrook, Armin Furrer, Wilbur Watkins, Leo Harryman, and Ronald Sellars.

[27] Before Mount Washington's surroundings were designated a wilderness area in 1964,[7] the Willamette National Forest administration had planned to open them to commercial timber production to address a shortage in Lane County, asserting that the land had little aesthetic or recreational merit.

[31] Mount Washington forms part of the High Cascades physiographic region in central Oregon, an arc of Pliocene to Quaternary lava flows, cinder cones, and fissure vents that trend from north to south,[11] with occasional large stratovolcanoes.

[32] Near Mount Washington, the High Cascades form a lava field with high-alumina, diktytaxitic basalt erupted from cinder cones.

These volcanoes have been eroded by glaciers and reduced to buttes in the Cascade arc, and much of the vents in the area were covered by Mount Washington.

Some basalt lava flows occur on the edges of Mount Washington at the Cache Creek and Dry Creek canyons or as outcrops that form benches (long, relatively narrow strips of relatively level or gently inclined land bounded by distinctly steeper slopes above and below) about 9.9 miles (16 km) away from Washington from Patjens Lake to the McKenzie River.

[33] Mount Washington is also part of the Sisters Reach subsegment, which extends for 56 miles (90 km) and contains at least 466 volcanoes that were active during the Quaternary.

Washington represents one of 30 mafic (rich in magnesium and iron) stratovolcanoes and shield volcanoes in the group, which include Pleistocene and Holocene eruptive centers.

[34] The volcano and its wilderness area sit on a lava platform with an altitude of 4,000 to 5,000 feet (1,200 to 1,500 m), and they are bounded by faults to the east and west.

"[37] In his argument for classifying Mount Washington as a stratovolcano, Hildreth adds that it is made of composite materials with steep slopes and a high relief of 2,300 to 4,300 feet (700 to 1,300 m).

However, Hildreth acknowledges that there is morphological continuity from steep mafic cones into transitional, cone-shaped shield volcanoes like Olallie Butte.

[1] The summit formed over a platform of basaltic andesite lavas from early eruptions at Mount Washington, made of thinner flows combined with pyroclastic rock.

[41] In the late Pleistocene, large glaciers extending more than 7.5 miles (12 km) to the east and west carved cirques into the slopes of the volcano.

About one mile in length, they trend northeast, with their mid-section parallel to depressions in the Cache Creek valley between Mount Washington and Blue Lake Crater.

[47] Otherwise, the Mount Washington and North Sister basaltic andesites display lithologic similarities[48] including a dearth of pyroxene phenocrysts and augite microphenocrysts,[49] and both groups were probably near-primary melts.

[38] Harris (2005) estimates that it has not erupted for more than 250,000 years, similar to Mount Thielsen;[5] this date is supported by James, Manga, and Rose (1999).

[1] Compared to larger stratovolcanoes in the Cascade volcanic arc, Mount Washington, like the rest of Oregon's Matterhorns, had a relatively short eruptive life.

[33] Several spatter cones produced basaltic andesite[1] on the lower northeastern side of the volcano,[52] following a fissure that reached 2.5 miles (4 km) from Washington's summit.