Geology & climate

Active geologic forces and moderate climate shape natural history and our coastal beauty.

On the leading edge of North America, the coast is shaped by dynamic forces as a continent moves west. In the southwestern corner of Oregon, the Klamath Mountains are remnants of ocean bottom, scraped up by North America between 280 and 100 million years ago and accreted in a process known as suturing.

Inland 100 miles, the Cascadia region gives evidence of a shift at the continent’s edge that allows the ocean’s tectonic plate to slip under the continent as the land mass moves west. Melted at depth, the molten rock rises to the surface through cracks and emerges as volcanic mountains starting 40 million years ago.

The local result of tectonics is the Coast Range, consisting mostly of sandstone and sedimentary formations scraped off the Oceanic Plate mixed amid areas of melted ocean-bottom basalt that emerged sporadically (60-12 million years ago).

Over the last 230,000 years, the land has continued to experience tectonic activity, and seawater has frozen and melted, to drastically change the sea level and the location and shape of the shoreline. The most noticeable remnant of those changes are the marine terraces which can be observed along the Oregon Coast (such as the one above Old Town Bandon), cut by the sea 80,000-100,000 years ago. During the Ice Age 20,000 years ago, "sea level" was more than 300 feet lower than it is today and the shoreline waves crashed a few miles west of today's beach. Today’s shoreline is only about 6,000 years old.

The combination of low, north-south mountains and the nearby Pacific Ocean give the Oregon Coast its trademark climate. Prevailing winds spread the sea's moderate, moist effects inland toward the mountains. On the Oregon Coast, the mean temperature in January is about 50° F; the mean temperature in July is about 65° F. At low elevations, daily temperature is also relatively stable. Annual rainfall on Oregon beaches averages 60-70 inches. Distance from the sea and elevation above sea level significantly affect local climate. In general, the summer highs get hotter and the winter lows get colder as you travel inland, and precipitation increases with elevation (to well over 100 inches on taller coastal mountains).

Our winds shift with the seasons-cool north winds in summer, warm south winds in winter-further moderating the temperature and driving the seasonal rainfall. Western Oregon has wet winters and dry summers, with only 10% of the annual rain falling from June through September. On the coast and in the mountains, geology shapes climate and both shape the diverse habitats and cultures of the Oregon Coast.