AMP: Pacific Hwy #1/5 Location: I-5 and Old Hwy 99, Jackson Cty Just after the old 99/OR 273 split, we’ll summit Siskiyou Mountain and reach the highest elevation on Interstate 5. AMP: 6 Location: I-5 and Old Hwy 99, Jackson Cty A mile later, exit again for Oregon 273, which continues to parallel I-5 along old 99, heading … Continue reading Interstate 5, OR 273 to OR 273