Siskiyou Summit is a mountain pass

Mountain pass

A mountain pass is a route through a mountain range or over a ridge. If following the lowest possible route, a pass is locally the highest point on that route...

 that carries Interstate 5

Interstate 5

Interstate 5 is the main Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific Ocean coastline from Canada to Mexico . It serves some of the largest cities on the U.S...

 (I-5) through the Siskiyou Mountains

Siskiyou Mountains

The Siskiyou Mountains are a coastal mountain range in the northern Klamath Mountains in northwestern California and southwestern Oregon in the United States. They extend in an arc for approximately from east of Crescent City, California northeast along the north side of the Klamath River into...

 near the border between the U.S. state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

s of California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 and Oregon

Oregon

Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

. The summit is located on the Oregon side, approximately 4 miles (6.4 km) north of the state line, and, at 4310 feet (1,313.7 m), is the highest point on Interstate 5. The pass features some of the steepest grades in the Interstate Highway System

Interstate Highway System

The Dwight D. Eisenhower National System of Interstate and Defense Highways, , is a network of limited-access roads including freeways, highways, and expressways forming part of the National Highway System of the United States of America...

. Siskiyou Pass is also crossed by the Central Oregon and Pacific Railroad

Central Oregon and Pacific Railroad

The Central Oregon and Pacific Railroad is a Class II railroad operating between Northern California and Eugene, Oregon, United States. It was previously a mainline owned by the Southern Pacific Railroad between Eugene and Weed, California via Medford, Oregon...

, originally the main line of the Oregon and California Railroad

Oregon and California Railroad

The Oregon and California Railroad was formed from the Oregon Central Railroad when it was the first to operate a stretch south of Portland in 1869. This qualified the Railroad for land grants in California, whereupon the name of the railroad soon changed to Oregon & California Rail Road Company...

. It was bypassed by a shorter and less steep route via Klamath Falls

Klamath Falls, Oregon

Klamath Falls is a city in Klamath County, Oregon, United States. Originally called Linkville when George Nurse founded the town in 1867, after the Link River on whose falls this city sat, although no falls currently exist; the name was changed to Klamath Falls in 1892...

, known as the Natron Cutoff, in 1926.

"Siskiyou Summit" is distinct from the "Siskiyou Pass

Siskiyou Pass

Siskiyou Pass is the highest point on Oregon Route 273 also known as Old Highway 99 and is distinguished from Siskiyou Summit on Interstate 5....

" that was the highest point of U.S. Route 99

U.S. Route 99

U.S. Route 99 was the main north–south highway on the West Coast of the United States until 1964, running from Calexico, California, on the U.S.-Mexico border to Blaine, Washington, on the U.S.-Canada border. It was a route of the United States Numbered Highways, assigned in 1926 and existing...

. U.S. Route 99 was replaced by Interstate 5 by 1964 but the pass on I-5 is commonly also referred to as "Siskiyou Pass".