NORTHWESTERN SECTION - Yellowstone Treasures - page 43

When it was flowing slowly, the lava's temperature would have been about 1,200°F
(650°C). Where the moving surface cracked apart, it would have glowed a bright orange
until cooled by the air.
The northern edge of the Madison Plateau is where Firehole Canyon Drive begins, but
the plateau extends southwestward about 30 miles (50 km) to the Idaho boundary. Ima-
gine the number of flows and the total amount of lava that must have flowed to create this
massive plateau.
The slow movement of rhyolite to form the Madison Plateau contrasts sharply with the
massive explosive eruptions that resulted in the Yellowstone Caldera. It was the caldera
floor onto which the rhyolites later flowed.
(2.0) (2) Swimming area—one of two places near park roads where the water is really warm
enough for swimming. (Read about the other on pages 255-56. ) The water of the Firehole
here is a pleasant temperature—about 75°F (24°C), neither warm nor cold. However, the Park
Service keeps this area closed to swimming until the water is low enough to be safe, usually in
July.
A stairway and a couple of rocky paths lead down to the water. There's no lifeguard on duty,
but park rangers check the area periodically. If you choose to swim here, you should keep your
head out of the water entirely, to avoid contact with harmful microorganisms. (See page 256
for details.) You will not be lonely: about 50 cars were parked along the road one recent warm
July afternoon. The restrooms on the side of the road away from the river are large enough for
changing clothes.
(2.2) Just before Firehole Canyon Drive rejoins the Grand Loop Road, a sign announces
“Firehole Cascade.” A blocked-off stretch of former highway provides a short walkway to the
best of the cascades and to fishing access, for fly fishing only. Parking is along the side loop
road.
Continuing on the Grand Loop Road 2.4/14.6 Note the “small, almond-shaped” island just
above the Firehole Cascades, as mentioned in Harry J. Norton's 1873 guide, Wonderland Il-
lustrated. Here, according to Norton, two members of his party camped for the night and re-
turned in the morning “with glowing descriptions of the sighing and singing of the merry
water-sprites who lulled them to sleep in their island couch….”