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

EVANS CREEK DRIFT

Between about 25,000 and 15,000 years ago Mount Rainier and the adjacent mountains were again buried by large glaciers; these glaciers formed the Evans Creek Drift, which consists of till as well as stream-deposited sand and gravel. These glaciers developed during an early part of the last major glaciation of the Pleistocene (Ice Age); at that time lateral moraines were deposited along the margins of glaciers high on the sides of some valleys and even along the crests of some divides, as at Ricksecker Point (fig. 4, locality 6) and Rampart Ridge. Till in the moraines is generally very coarse, loose or slightly compacted, and as much as 50 feet thick. The till is mostly gray or purplish gray, but it has a yellowish-brown oxidized zone in the upper 2 or 3 feet that has been formed by weathering processes since the till was deposited. Stones in this oxidized zone rarely have weathered rinds. Evans Creek till is especially well exposed in roadcuts along the north side of the White River valley east of Yakima Park (fig. 4, locality 7).

At the time the Evans Creek Drift was deposited, ice fields and glaciers mantled the slopes of the volcano above an altitude of about 5,000 feet. Each major valley was occupied by a glacier 1,000—1,500 feet thick which extended from 5—35 miles beyond the park boundaries (fig. 9).

MUDFLOW AT VAN TRUMP PARK

Trump Creek northeast of Comet Falls. The mudflow is widespread in areas beyond an end moraine of Van Trump Glacier that probably was formed about 11,000 years ago, but it does not overlie the moraine itself and thus is older.

Between 11,000 and 15,000 years ago a large landslide of rock from the summit of Mount Rainier swept down the south flank of the volcano and spread as a mudflow over Van Trump Park. There it deposited a yellowish-orange unsorted mixture of clay, sand, and rock debris which is as much as 6 feet thick on the ridgetop at Van Trump Park (fig. 4, locality 8) and is 20 feet thick in the valley of Van Trump Creek northeast of Comet Falls. The mudflow is widespread in areas beyond an end moraine of Van Trump Glacier that probably was formed about 11,000 years ago, but it does not overlie the moraine itself and thus is older.

EXTENT OF GLACIERS at Mount Rainier and in the adjacent mountains during the most recent major glaciation is shown by stipple pattern. The heavy black line at the upper left marks the boundary between the Puget Sound lowland and the Cascade Range. This line also represents the southeast edge of a massive glacier in the lowland which originated in southwestern Canada and reached this part of the lowland about 14,000 years ago. The arrows show the direction of glacier movement. Black areas are covered by glaciers today. (Fig. 9) (click on image for an enlargement in a new window)

McNEELEY DRIFT

McNeeley Drift, named in this report, consists of till in moraines formed during the latest part of the most recent major glaciation, probably about 11,000 years ago. The name of the drift is taken from McNeeley Peak, which is north of Yakima Park. A typical moraine lies within a north-facing cirque half a mile south of the peak (fig. 4, locality 9). Weathering extends to a depth of 15 inches or less in the till, and stones in the till that have been decomposed by weathering processes are rare. McNeeley moraines are found adjacent to some large active valley glaciers on Mount Rainier and in some cirques at altitudes between 5,500 and 6,700 feet. Areas in front of cirque moraines generally consist of either glacier-scoured bedrock or feature less Evans Creek Drift. McNeeley moraines are sharp crested and little modified by erosion. They range from single low narrow ridges of till to accumulations as much as 1,000 feet wide that are distinguished by multiple ridges. One of the largest McNeeley moraines dams Mystic Lake on the north side of the park, and the Wonderland Trail crosses another at the south end of Berkeley Park (fig. 4, locality 10). A small McNeeley cirque moraine can be seen along the highway between Tipsoo Lake and Chinook Pass (fig. 4, locality 11).