Wow, you do seem to find huge rootstocks. Probably the only place to find bigger root stocks is on the Big Basin map.
Yes, Big Basin may be worth a visit since there is something about rootstocks which intrigue me. :) There was a very large twin that I should have taken a picture of. It was pretty cool too.
The Mariposa redwood grove in Yosemite had some contenders as would any redwood grove. I recall a sign indicating that the fallen redwoods stay around hundreds of years. Peggy told me of some o-maps in the Seattle area which might qualify--they always map the trunk direction since they are such an obstacle. Was this one in Meadowood?
This one was on the Fountainhead map.