It is also a popular tourist destination despite its remoteness, with recreational activities including hiking, backpacking, mountaineering, and photography.

Also known as Seekseekqua by Native American populations, the volcano was named after United States President Thomas Jefferson, and was first ascended by E. C. Cross and R. L. Farmer in 1888.

Despite the low chance of future eruptions, many scientists still consider mudflows a major threat at Mount Jefferson.

[16] These breach events yielded floods and small lahars (volcanically induced mudslides, landslides, and debris flows).

[19] The volcano, like much of the Oregon Cascades, was likely covered by an ice cap during the Pleistocene,[20] with the glaciers at their peak size between 25,000 and 20,000 years ago.

[19] Other geographic features at Jefferson include rock outcrops, steep talus slopes, conifer forests, and alpine meadows.

[30] Above the timber line at 7,200 feet (2,200 m) above sea level, mountain hemlock and whitebark pine predominate,[13] though mountain hemlock has also invaded into subalpine meadows at Mount Jefferson,[31] possibly as a result of fire control programs, grazing, the influence of adjacent forest areas, and climate change.

[34] Other bird species found in the area consist of Eurasian three-toed woodpeckers, willow flycatchers, olive-sided flycatchers, tree swallows, Canada jays, Steller's jays, common ravens, Clark's nutcrackers, black-capped chickadees, mountain chickadees, chestnut-backed chickadees, red-breasted nuthatches, pygmy nuthatches, Eurasian treecreepers, American dippers, wrens, American robins, varied thrushes, hermit thrushes, Townsend's solitaires, golden-crowned kinglets, ruby-crowned kinglets, water pipits, blue-headed vireos, western tanagers, Cassin's finches, gray-crowned rosy finches, pine siskins, red crossbills, green-tailed towhees, dark-eyed juncos, white-crowned sparrows, golden-crowned sparrows, fox sparrows, and Lincoln's sparrows.

These extensional processes formed grabens, or valley-like depressions between parallel fault lines, at the eastern boundary of the central Cascades, including a 4,000-foot (1,200 m) deep formation.

With a width of 16 miles (25 km), it differs from the adjacent northern segment of the Cascades, where volcanoes show a scattered distribution.

[40] The melting of the metamorphic rocks amphibolite and at deeper strata, granulite, have both produced intermediate and silicic lavas at Jefferson.

[36] The strip may still be active, as monogenetic vents near Jefferson have produced basaltic andesite since the last glacial period.

[40] Jefferson — with Mount Hood, the Three Sisters-Broken Top area, and Crater Lake — represents one of four volcanic centers responsible for much of the Oregon Cascades' Quaternary andesite, dacite, and rhyolite deposits.

[46] Between five and six million years old, the field reaches north from Jefferson to Olallie Butte,[47] and it covers an area of 58 square miles (150 km2).

[49] The field is also likely underlain by a batholith, a large mass of intrusive igneous rock (also called a pluton) that forms from cooled magma deep in the Earth's crust.

[4] Rhyodacitic lava flows and pyroclastic material, which have since been significantly altered and stripped by glaciation, originated from eight vents in the area.

[56] The area is full of cinder cone volcanoes and intrusive lava plugs, which occur in irregular patterns.

[50] Scientists lack a comprehensive record of activity at Mount Jefferson, as important details have been obscured by the erosion of deposits by large glaciers.

[60] Instead, they formed lava tongues near the crater and coursed down spaces in between glaciers, creating volcanic glass and columnar joints, or arrays of prismatic shapes.

A huge explosive eruption took place between 100,000 and 35,000 years ago[59] (scientists have been unable to create a more specific time frame for the event),[8] producing ash layers that covered the Metolius and Deschutes River valleys and eventually extended to the city of Arco, in the southeastern part of the state of Idaho.

"[63] In a 1987 report, Richard P. Hoblitt and other USGS scientists estimated that the yearly likelihood for a major explosive eruption at Jefferson does not exceed 1 in 100,000.

[65] An eruption from the volcano would threaten the immediate surrounding area, in addition to places downstream near river valleys or downwind that could be affected by ashfall.

Moreover, while basaltic lava flows from surrounding monogenetic vents tend to travel slowly and typically only reach 12 miles (19 km) from their source, and therefore would not pose serious hazards to much wildlife or humans, they would still burn and bury anything they encountered.

[67] Moreover, ash can cause irritation of the eyes or respiratory system among the ill, the elderly, and infants, potentially leading to chronic lung disease.

[75] Field work followed in summer during 1965, led by G. W. Walker, and a 1974 study of the volcano's glacial and volcanic history was carried out by Kenneth G. Sutton and other geologists.

George J. Pearce, who accompanied Cross and Farmer on the expedition, wrote an account of the climb for the Oregonian newspaper on 22 August 1900.

Still, the mountain and its surrounding wilderness are visited by so many hikers, backpackers, and climbers each year, especially during the summer, that they face threats to their ecological well-being.

[6] The Warm Springs Tribal Council does not permit access to the volcano's eastern side, so only the western flanks can be used by the public.

[78] Located within the Mount Jefferson Wilderness, it represents a popular tourist destination for its views, lakes, and meadows, with activities including backpacking, climbing, and hiking during the summer, as well as nature photography.

[79] As a result of increased traffic to the area between 2012 and 2014, the Willamette National Forest administration enforced a campsite reservation system as of 2016, but stopped the practice in 2017 due to its failure to reduce human impact within the region.