My first hunch was that this was photographed from Guys Peak, that cross between a pyramid and a pile of sugar (during the winter) that rises abruptly over Snoqualmie Pass. But now I figure this view looks south and a little east from the southern slopes of Denny Mountain (and the then still future Alpental ski runs and lifts) over the Pass to Lake Keechelus.
Your second assessment seems spot-on to me, as I google it. There is a lower knob, the southeasternmost shoulder of Denny Mountain, where the vistas match up precisely. It’s interesting to note how the highway’s path has changed since HS’ photo but its former “meanders” are still visible in the current network of roads at the pass.