On the morning of our last day at Yellowstone, we awoke at Old Faithful to find brooding, moody skies overhead. We set off to two of the smaller geyser basins -- Biscuit Basin and Black Sand Basin -- to check out the geothermal features there.
Early in the morning at Biscuit Basin, I spied some geese among the puffs of steam coming from this small pool, which I don't believe is a hot spring itself but collects run-off from other springs. Wildlife at Yellowstone often makes use of the heat produced by hot springs to keep themselves warm when the weather gets chilly -- especially in the winter. Some day I need to get back here in the winter...