The last time I was in Yellowstone National Park was roughly
1985, right between my 8th and 9th grades. At that time,
Yellowstone was a percolating gaggle of geysers, mudpots, steam
vents, mineral wells and all sorts of other sulphur-scented
yummies. However, this time around, nothing was happening at all.
The huge water pools that my dad and I both remembered vivdly
were dry as a bone with grass growing from them, which meant (at
least to me) that they'd been dormant for some time. The white
crystalline waterfall at Mammoth Springs had turned brown,
and was just barely trickling (see picture above).
The park was so empty that we couldn't find a park ranger to ask,
so we're assuming the lack of geological activity was due to the
cold weather (there was 12 feet of snow on the road entering the
park), and hopefully not due to humans screwing things up
environmentally, as usual.
Anyhoo, to learn more about Yellowstone, check out the Yellowstone National Park
website.
The ride out of Yellowstone was a bit unnerving. Since there was so much snow, and since Yellowstone is in the middle of the mountains, many of the roads out of the park were closed, since the mountain passes were snowed in. There was one pass that was open (or rather, we didn't hear that it wasn't open, so we took a shot), called Chief Joseph Memorial Highway, which was a gorgeous scenic route through the mountains. Well, it was scenic until we were whited-out... the fog was so thick, and the snow was so deep around us that we could hardly see in front of us. Here's a shot out the front of our car.

Needless to say, we were happy when we got below the clouds again!