mountains. The settlement of the valley has spread out across the lowlands; developers, taking advantage of the "cheapest" landscape, displace farms along the way. The Tualatin Plains are separated from the Yamhill River by the Cheha- lem Mountains, which act as an additional buffer from the moisture-laden storms passing through the Coast Range. At the peak of the mountains the annual average rainfall is 54-55 inches, whereas only several miles northeast near Aloha on the Tualatin Plains, the annual average rainfall is 38 inches. Compare this to downtown Portland with an annual average rainfall of 46 inches. Oregon City Past the junction of the Tualatin River, the Willamette Valley narrows down to ♦ a few miles in width. On the west the Chehalem and Tualatin Mountains come close to the river's edge, while on the east a ridge of the Cascades, which separates the Molalla and Clackamas river watersheds, comes close to the shore of the river as it falls 30 feet at Oregon City. Here both salmon and settlers have come to rest; the salmon do not naturally make it past the falls, and the settlers stopped here, forming Oregon's leading city in the 1840s. But Oregon City was not destined to continue its primary role due to its restricted physical site and inaccessibility by river for larger boats. Oregon City is the southern gateway into the Greater Portland area and, because of prevailing wind patterns, has some of the highest air pollution readings in the area. Clackamas River As we move downriver from Oregon City, the Tualatin Mountains begin to take hold of the landscape on the west side of the river; on the east side the Clackamas River joins the Willamette. The Clackamas passes mostly through a narrow channel, seldom given a chance to meander in its 80-mile journey. The town of Estacada, 30 miles southeast of downtown Portland along the Clackamas River, is the last outpost before the Cascade Mountains. The climate of Estacada is a far cry from downtown Portland, with 100 fewer days in the growing season and 15 inches more annual rainfall. Above the Clackamas on the north and south are plateaus punctuated by higher hills. On the south is an open prairie area which in former days was referred to as Horse Heaven Ridge. Just west of Mclver Park is an excellent viewpoint of the brief Clackamas River Valley. To the north of the Clackamas, the westward expansion of Portland creates an incongruous mix of berry farms, tree nurseries and post World War II housing developments. Both plateaus, especially Horse Heaven Ridge, are under the influence of the Columbia Gorge winds, and both have more rainfall and snow accumulations than the city of Portland. Gresham, for example, several hundred feet above the elevation of downtown Portland, experiences about 55 inches of rainfall annually. Columbia Gorge The Columbia Gorge commences graphically at Troutdale, a small community just above the Columbia River floodplain and at the confluence of the Columbia and Sandy rivers. West of Troutdale, the east wind, as it is simply referred to, fans out over the flatlands of suburban east Portland. During January the wind can sweep through Portland, trapped between the bluffs north and east of Vancouver, Washington, and the hills of far southeast Portland (Mt. Scott, Kelly and Powell buttes), rush toward the Tualatin Mountains and (sometimes) bully its way over the Tualatin Plains and clear across the Coast Range. But more often 23 David Brown
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