pockets of lodgepole and ponderosa pine. Atmospheric pressure differentials east and west of the Cascades create a wind tunnel effect in the deep cut of the gorge, generating winds that make it a popular windsurfing and kiteboarding location. It also creates the right conditions for snow and ice storms during the winter months which also draw very cold east winds toward the mouth of the gorge on the west end. The gorge is a popular destination for hiking, biking, sightseeing, fishing, and water sports. The area is known for its high concentration of waterfalls, with over 90 on the Oregon side of the gorge alone. Many are along the Historic Columbia River Highway, including the notable Multnomah Falls. Trails and day use sites are maintained by the Forest Service and many Oregon and Washington state parks. Geology The Columbia River Gorge began forming as far back as the Miocene (roughly 17 to 12 million years ago), and continued to take shape through the Pleistocene (2 million to 700,000 years ago). During this period the Cascade Range was forming, which slowly moved the Columbia River's delta about north to its current location. Although the river slowly eroded the land over this period of time, the most drastic changes took place at the end of the last ice age when the Missoula Floods cut the steep, dramatic walls that exist today, flooding the river as high up as Crown Point. This quick erosion left many layers of volcanic rock exposed. Ecology The Columbia River Gorge is home to a number of plant species that are endemic or found mostly in the gorge and surrounding areas, including Heterotheca villosa, Lomatium columbianum, Lomatium klickitatense, Lomatium suksdorfii, Penstemon barrettiae, and Primula poetica. History The gorge has supported human habitation for over 13,000 years. Evidence of the Folsom and Marmes people, who crossed the Bering land bridge from Asia, were found in archaeological digs. Excavations near Celilo Falls, a few miles east of The Dalles, show humans have occupied this salmon-fishing site for more than 10,000 years. The gorge has provided a transportation corridor for thousands of years. Native Americans would travel through the gorge to trade at Celilo Falls, both along the river and over Lolo Pass on the north side of Mount Hood. In 1805, the route was used by the Lewis and Clark Expedition to reach the Pacific. Early European and American settlers