I am not Dick Davies but I will add a little input here. About
seventeen years ago the San Francisco rock club took us on a field
trip down on the bay in the rip rap at Berkley to look for agates.
The original site they came from was not acessable. The agates were
there… little amydules that had filled bubble holes in lava. But
there wasn’t a single redeeming feature that made them useful or
beautiful. Just little translucent blobs of white chalcedony.
There are old accounts of iris agate being found on the eastern side
of the slope (Oakland?) above and to the north of the tunnel on the
highway that goes over to Livermore. What its status is now, I cannot
say. At that time there were no houses on it, but it was a steep,
fenced off area. Do your homework on property ownership before
venturing over the fence. Come to think of it, it might be a little
embarrasing to explain the the CHP how you ended up plopping down on
a car coming out of the tunnel!