The base of the waterfall above the BC Hydro Hydroelectric plant by Herrling Island is supposed to have some cool agates and stuff.
That site has big quartz crystals. The good site for agates is up at Goldpan Park on the Thompson. Neither is a good hiking site especially.
Good hiking with rockhounding destinations would be Red Mountain Mine in Slesse Creek; Copper Mound near Tenquille lake; Gray Rock Mine near Mt Truax; Eureka Mine below Isolillock; Silverdaisy Mine of course. Much of the South Chilcotins, especially Cinnabar Basin. And of course Slumach's Lost Gold [8)][}][)]
on the sides of the old logging roads above harrison lake, you can find TONS of fossils. I can't remember the exact directions to the place, but I'll see if I can find them
KM 29, at the base of the boulder talus near the cliffs on the East side of the road. It's easy to spot because it looks like a quarry. The Hale creek road is also a good spot, and a bit of a hike from the main road.