They extend in an arc for approximately 100 miles (160 km) from east of Crescent City, California, northeast along the north side of the Klamath River into Josephine and Jackson counties in Oregon.

Western canyons can receive over 100 inches (2,500 mm) of rain in some winters and are densely forested, while eastern areas are more arid.

[5] The greatly varied topography and climate contribute to high biodiversity, and the Siskiyous are noted for a number of endemic species.

The Cree were in the area as part of McLeod's Hudson's Bay Company expedition, and had been recruited far away in their homeland in eastern Canada.

[7] Another version, given in an argument before the State Senate in 1852, is that the French name Six Cailloux, meaning "six-stones", was given to a ford on the Umpqua River by Michel Laframboise and a party of Hudson's Bay Company trappers in 1832, because six large stones or rocks lay in the river where they crossed.

[8][9] According to some, the Six Cailloux name was appropriated to this region by Stephen Meek, another Hudson's Bay Company trapper who was known for his "discovery" of Scott Valley, in regard to a crossing on the Klamath River near Hornbrook.

[13] Most early exploration of the area came from the coast, beginning in 1775, when the Spanish lieutenant Bruno de Heceta came to the Northwest.

Originally based on existing Native American foot trails winding their way through river valleys, the Siskiyou Trail provided the shortest practical travel path between early settlements in California and Oregon in the 1820s.

The large and sudden influx of white population deteriorated the relationship with the natives in the area.

[19] Irrigation projects that began at the end of the 19th century led to a boom in the fruit orchard industry.

In addition, the pass includes several hazardous curves, and is frequently hit with snow, ice, and fog during winter storms.

In winter, it is common for the highway to be closed one to four times per year by transportation authorities because of hazardous conditions.

[citation needed] The climate of the mountains is distinctive in how it varies from the coast to the inland slopes.

[26] Fogs provide an additional source of water at low elevations near the coast, especially in summer.

Higher in the mountains and farther east, the temperatures range from overnight lows just above freezing to highs around 21 to 23 °C (70 to 73 °F).

Lawson's cypress (also known as Port Orford cedar, Chamaecypraris lawsoniana) occurs throughout the range west of the summit.

The subalpine forests above 5,000 feet (1,500 m) include mountain hemlock (Tsuga mertensiana) and Shasta red fir (A. magnifica subsp.

Other conifers include weeping spruce (Picea breweriana), an endemic species,[29] and coast redwood (Sequoia sempervirens).

[29] Mammals in the area include small rodents, deer and elk, and bear and coyote.

[42] Another rare animal is the fisher, a predatory medium-sized mammal that lives in old-growth forest.