[4] When the highway was rebuilt on its current alignment, road cutting lowered the elevation of the summit by 49 feet (15 m).

[5] The Siskiyou Mountains form the watershed boundary between the Klamath and Rogue Rivers and are also a rough natural separator between Oregon and California.

[6] The road over Siskiyou Summit is typically closed to traffic for many days during winter due to severe weather conditions.

Snow generally falls during the months of November through April, typically peaking with four such days in December.

[8] The Hudson's Bay Company carved a route from Oregon to California during their hunt for furs and pelts following Native American trails.

Since the gradient is about 6%, it is a preferred place for truckers to park, refuel, check the condition of their vehicles, and rest.