Supposedly this is on BLM (Bureau of Land Management) land so it would be open to public collecting.  Here is the information posted in 2004 from T. McGinnis:

"What: Agate, dendrites, moss agate and sometimes angel wing.
Agency: Bureau of Land Management
Tools: Rock hammers, picks and shovels only.
Note: Diggings are mostly at the base of the rim. Beautiful float found from
mountain skirt a base of rim rock to the flat below. Hard digging. Mostly
agate with rhyolite.
CAUTION: There are private claims throughout this area, but open BLM lands
surround these claims."

Directions from T. McGinnis: "Take Highway 380 Post/Paulina to milepost 14, to monolith on
right. Turn right at the second road. The distance to the site is short but
sharply inclined and rough.  Beautiful float found from
mountain skirt a base of rim rock to the flat below."

I can't gather the exact spot from that, but I'm marking the GPS coordinates at the Eagle Rock monolith.