Syncline Mountain is a 7,560-foot summit in northern Washington on the border of Okanogan and Whatcom counties, within the Okanogan Range of the North Cascades and the Okanogan–Wenatchee National Forest. Unofficially named for a prominent folded rock formation, it is identified by a conspicuous syncline. The Pacific Crest Trail crosses its east slope, with the summit reached by an off-trail scramble. Its runoff drains east toward Trout Creek and the Methow River and northwest toward Slate Creek in the Skagit basin, marking a divide. The mountain also reflects the larger geologic history of the North Cascades, shaped by uplift, faulting, volcanic activity, terrane accretion, and Pleistocene glaciation.