Geological Survey Bulletin 1288 Surficial Geology of Mount Rainier National Park Washington

TRAVERTINE

Travertine is a calcium carbonate mineral that has been deposited by the water of warm or hot springs. Deposits of yellowish-orange to white travertine of unknown thickness that underlie parts of a meadow at Longmire and a small area near Ohanapecosh campground have been formed by warm spring water that still issues from the ground at both localities. Pumice layer W is interbedded with the travertine near Ohanapecosh campground.

ALLUVIAL CONES

Alluvial cones are steeply sloping, poorly sorted stream deposits of loose rock debris which lie beneath cliffs and are wedge shaped in ground plan (fig. 18). Their surfaces are scarred by one or more gullies, the sides of which are paralleled by low bouldery ridges 5—25 feet wide and 3—10 feet high. Some cones seem to consist chiefly of rock fragments larger than 6 inches in diameter, but others are rich in debris of sand and pebble sizes. Very large blocks lie on the surface of some cones. Alluvial cones are distinguished from taluses by less steep slopes, by a markedly decreasing slope toward the toe, and by stream-gullied surfaces. Most cones head at the mouths of steep rock-walled gullies and have been formed by small streams and mudflows that descend the gullies during rainstorms. From Ricksecker Point, a typical alluvial cone can be seen on the opposite side of the Paradise River valley (fig. 4, locality 30), and the West Side Road crosses one at the base of Mount Wow (fig. 4, locality 31).

ALLUVIAL CONE at the east base of Mount Wow. The largest blocks in the deposit are about 20 feet in diameter. (Fig. 18)

ALLUVIUM

Alluvium includes both unvegetated sand and pebble-to-boulder gravel deposited by modern streams and rivers and the same type material underlying forested terraces or benches as much as 15 feet higher than the stream channels. Some low terraces contain poorly sorted bouldery deposits that may be mudflows or alluvium transported by floods. Near the ends of present glaciers, alluvium locally includes lenticular mudflows a few feet thick that came from moraines or from rock debris on the glaciers; boulders larger than 5 feet in diameter in the alluvium probably were carried by these mudflows. Nearly all the alluvium shown on the geologic map has been formed within the last 500 years.