The Continental Divide is the topographic line that separates Pacific and Atlantic Ocean drainages, running in North America down the spine of the Rocky Mountains between Alaska and Mexico along the highest points between the drainages. At an elevation of 12,095 feet above sea level, Highway 82 over Independence Pass is the highest paved road crossing of the Continental Divide in North America. This location also marks the boundary between Lake County and the Pike-San Isabel National Forest to the east, and Pitkin County and the White River National Forest to the west. The Grizzly Tunnel brings water from the Roaring Fork and Lincoln Creek drainages under the Continental Divide to Lake Creek, the source of Twin Lakes, and changes in flow due to diversions have damaged both Lincoln and Lake Creeks. The Roaring Fork River is the second-largest tributary to the Colorado River in the state, with some of its flow diverted east under the Continental Divide through the Twin Lakes Diversion System. The Continental Divide is also identified as a geographic designation running along the highest points between Alaska and Argentina, separating the Atlantic and Pacific watersheds, with land in North America west of the Divide draining to the Pacific Ocean and land east of it draining to the Atlantic Ocean. In the mid-1960s, tons of snowfence were built around the pass in an experiment to capture more winter snow and increase runoff, but the experiment failed and the snowfence was abandoned on surrounding ridges until the Independence Pass Foundation led a successful effort to remove the debris that was smothering tundra plants and creating a hazard to hikers and skiers.