This map from an old field trip brochure shows where gold has been found along the Santiam river, Green Peter reservoir, and in the immediate area. They say to look where you've found gold before, so looking at old maps of old mining claims is worth the time. See map below, or view it in the full document on page 100. (Click on map for full size image).
It would be worth looking into where you can pan legally in this area today and if a permit is required.