The Lower Geyser Basin is another such detail. Hot springs line both sides
of the river and the Firehole receives thermal runoff from such features
as Ojo Caliente, Great Fountain Geyser, and the River Group.
Also, many tributaries of the Firehole are also thermally influenced
and contribute additional hot water or chemical changes. By the time the
river has finished its run through the Upper, Midway, and Lower Geyser
Basins, approximately a quarter of its water comes from geysers
and hot springs—and there’s nothing minor about that!
The famous trapper, Jim Bridger, thought the Firehole River was warm because
the water flowed so rapidly across its bed that it was heated by friction.
Now we know the real reason!
The Lower Geyser Basin marks the end of the thermal areas. After this
point, the river starts to cool though it never regains its original temperature.