Geologic Guide to the Deer Park Area
NPS Logo


The Mountain Glaciers


Running water is the dominating agent of erosion today in the Deer Park area, but the visitor to Blue Mountain does not have to look far to see that the real tool which carved the mountains was ice. The cirque on the north side of Blue Mountain itself once contained a glacier, and today still retains winter snow far into the summer. To the south, the headwaters of all the major creeks are spotted with snow banks, feeble reminders of the numerous glaciers that once plucked the rock away to leave cirques. Although the largest glaciers in the Olympic Mountains are found farther west in the remote Mount Olympus area, the visitor to Deer Park can see a few small ones at the base of The Needles and at the head of Cameron Creek (fig. 4). These glaciers are the remains of larger bodies of ice, though it is probably not possible to trace their lineage clear back to the great Ice Age.

The Canadian Icecap

The most dramatic glacier story to be unfolded is not of the local (alpine) glaciers but of the great Canadian Icecap that at one time lay to the north, and few view points in the Olympics better allow the imagination to re-create the time of the Ice Age than does Blue Mountain. To the north we look out over the plains and waterways where lay the southern margin of the great Canadian Icecap about 15,000 years ago.


Perhaps overlooked by the traveler on the way up Blue Mountain, but worth looking for later on the way down, are large boulders of white granite along the roadside (at about 4.9 miles from Deer Park, or 3.0 miles from the Park boundary). As far as is known, there is no bedrock of granite anywhere in the Olympics. Thus these boulders must have been brought here by the Canadian ice. And, in fact, boulders of rock types characteristic of the North Cascade Mountains and British Columbia Coast Ranges are common up to elevations of about 3,500 feet all around the north and northeast end of the Olympic Mountains. We can visualize the great mass of ice pushing up and around the dam of the Olympics, one branch of ice flowing out along the Strait of Juan de Fuca to the sea, the other flowing south in the Puget lowland beyond the city of Olympia, where the ice finally melted as fast as it advanced.


To the northwest we can see tree-covered flats on a broad, low divide between the ridge of Blue Mountain and Round Moun12tain (point 12 on fig. 8C). The edge of the icecap pushed across this divide between the two mountains, for this area is covered with debris left by the icecap, and the slopes leading westward into Maiden Creek are likewise veneered with glacial outwash. In fact, even from Blue Mountain we can see rounded outcrops of lava on Round Mountain, smoothed by the scraping of ice. Round Mountain itself owes its shape to the work of the icecap which probably covered it for a time. Compare its smooth shape with the jagged unglaciated cliffs of Mount Angeles.

fig. 8A (top). Before ice age glaciation. Morse Creek flows east by Round Mountain. fig. 8B (middle). Ancient Lake Morse formed. fig. 8C (bottom). Morse Creek today. (click on image for a PDF version)

Ancient Lake Morse

The story, however, is not finished. More granite boulders are scattered throughout Morse Creek Valley, its tributaries, and all the other forested valleys west of Blue Mountain, up to an elevation of about 3,500 feet. Although we might imagine that these boulders, too, had been carried in by the icecap, we find no other evidence of the glacier having filled the valley, that is, no rounded knobs and smooth ridges as seen in other places overridden by the icecap.

But if there was no ice, how did the boulders get there? Can we not conclude that the valley was filled with a lake at the toe of the icecap (fig. 8B)? Could not icebergs, breaking off the ice, laden with foreign rocks and gravels, float out into the lake where they slowly melted and dumped their load of debris to the bottom far from the edge of the ice? Such ice barges have indeed been observed in present-day northern latitudes where icecaps and glaciers still reign. And it seems only logical that, with the icecap pressed close around the mountain front, the streams draining the mountain would be dammed. On the hillside below Round Mountain, we can find some evidence of this lake in mud deposits, typical of quiet lake waters at the fronts of glaciers.

A Change in the Course of Morse Creek


The icecap and lake can explain some of the landscape seen today, but there are still two peculiar features not so easily explained. One is at the head of Morse Creek, where the Cox Valley (fig. 1) is broad and flat, singularly different from the narrow high valleys of the Morse Creek tributaries.


A second is the odd bend that Morse Creek takes, as a glance at figure 1 will confirm. Flowing for several miles in an east-northeasterly direction, eroding its valley in the relatively soft shale and sandstone, it suddenly takes a sharp swing to the north and cuts through a thick ridge of resistant lava.

A drive up the Hurricane Ridge Road will impress upon the visitor the abruptness of this gorge. But look again at the low divide between Round Mountain and Blue Mountain. The divide is suggestively in line with Morse Creek's eastward course, and if we take the bends out of Morse Creek and chart the elevations of the creek bed along a line extending from its headwaters above the Cox Valley across the low divide, south of Round Mountain, we find that the divide lines up vertically as well as horizontally with the flat bottom of the Cox Valley (fig. 9). This suggests that the Cox Valley and the low divide are both parts of a once-continuous valley.

fig. 9. Elevations along the bed of Morse Creek. Dashed line shows course across the low divide.

To explain this change in the creek's course we might put all these observations together in a tentative and no doubt greatly simplified history. At one time, before the continental ice filled the lowlands to the north, Morse Creek flowed northeast around the south side of Round Mountain, thence out north to the Strait of Juan de Fuca (fig. 8A). Its position here was determined by a long history of erosion, during which time the relative hardness of the lavas of the Mount Angeles-Round Mountain ridge caused the ridge to stand out above the valleys eroded in softer rock.

When the icecap grew and advanced to block Morse Creek, a lake was formed which eventually spilled over the lava ridge just west of Round Mountain, probably following a course to the strait between the icecap and the mountain front (fig. 8B). When the icecap began to melt away, as world climates warmed up, Morse Creek was trapped. It had cut a notch in the hard lava ridge and was already lower than its old course across the low divide. As it cut an ever-deepening gorge through the lava, the lake drained away. And in fact, we must imagine the land rising to some extent as the great weight of ice was removed from it; thus the creek cut well below its ancient course. In a sense, the Cox Valley and the low divide south of Round Mountain are fossil remnants of the ancient Morse Creek Valley.

<<< Previous <<< Contents>>> Next >>>

Last Updated: 20-Aug-2010