I didn't notice this block of rock along the path from the parking area to the beach- or more accurately, paid no attention to it- because I was eager to go look at the conglomerate. This does not show the characteristic fracturing that pervades much of the Humbug Mountain Conglomerate at the beach level. It was clearly intentionally placed to block vehicular access, and I suspect it comes from elsewhere on the mountain.
Granitoid rocks are not common in Oregon. There are a few stocks exposed in the Western Cascades, for example, in the Quartzville area. Other than that, it's almost entirely restricted to the Klamath Mountains in southwest Oregon and the Blue Mountains in the northeast to north central portion of the state. In the sample above, you can pick out a number of granitic pebbles, so at least at some point in the past, such rocks were exposed in this drainage basin.