South Saddle Mountain, in the Tillamook State Forest of Oregon’s Coast Range, is the highest mountain in Washington County and the range’s eighth-highest peak. Its rocks record a long geologic history reaching back about 40 million years to the Eocene, with sandstone, siltstone, basalt flows, and basaltic sandstone shaping the mountain, and some nearby sedimentary layers forming about 20 million years ago. Once called simply Saddle Mountain, it was officially renamed in 1983 to distinguish it from another Oregon peak. Its lower peak holds a microwave transmission tower, while the forested slopes support birdwatching and off-road motorcycle use.