The Chalk Cliffs below Mount Princeton are not made of chalk

West of Nathrop, the bright white face below Mount Princeton catches the eye from the highway. People call it the Chalk Cliffs, and the name is a friendly mistake. There is no chalk in them.

What you are looking at is granite that has been changed by hot water moving through the rock over a very long time. That heat and water broke the granite down into soft, pale, crumbly material, which is why the slope looks white and washes into Chalk Creek below. Geologists call this kind of change hydrothermal alteration, and it is the same underground heat story that gives the area its hot springs. The warm water that surfaces near Mount Princeton and along Chalk Creek comes from the same deep source that bleached the cliffs.

For a new resident or a curious visitor, this connects a few familiar sights into one picture: the pale wall, the warm water, and the steam on a cold morning are all signs of heat in the ground here. It also explains why the cliffs are loose and prone to sliding rather than solid like the harder granite peaks above them, so the base is not a safe place to scramble.

To read the real geology behind the Chalk Cliffs and the local hot springs, see the Colorado Geological Survey’s reports on Chaffee County and on Colorado geothermal areas.