I-5 enters Oregon at the California state line in southern Jackson County. The highway travels northeast along a ridge in the Siskiyou Mountains, with a maximum grade of 6 percent, to Siskiyou Summit; at , it is the highest point on all of I-5 and one of the highest points on the Interstate system. The mountainous, section of the freeway runs along Siskiyou Pass and includes several runaway truck ramps and chain-up areas due to its heavy use by trucks and its foggy and snowy conditions in winter. North of the summit, the freeway intersects the Old Siskiyou Highway (OR 273) and the Pacific Crest Trail before it travels out of the Rogue River-Siskiyou National Forest.