We went to Calaveras Big Trees National Park. The kids have never seen the giant sequoias before and were suitably impressed. Charissa missed out since she's in school this year, and Robin missed out since she was camping in Yellowstone with a friend.
Here's the girls sitting on "The Big Stump" with the cut log end visible to the side. The grooves you can see were made by the miner's drills since there were no saws big enough to cut the tree. The tree was felled in order to take a cross section to San Francisco as a side show.
This next picture is of the kids standing in the bottom of a fallen tree. (Sorry for the blur.)
Here's Katie standing on a fallen log.
I have a few more pictures on Flikr here.