The valley is surrounded on the north, east, and south by mountains that form the continental divide, and thus it forms a slight pocket eastward in the drainage basin of the Pacific Ocean in this part of the Rockies. North Park, to the north, is drained by the North Platte River and separated from the valley by relatively low passes, Muddy Pass and Willow Creek Pass. The passes on the east (Milner Pass) and south (Berthoud Pass), connect to the basin of the South Platte River. They are both in the Front Range proper and thus are higher and more likely to be snow-covered. Milner Pass is near the height point on Trail Ridge Road (U.S. Highway 34 in Rocky Mountain National Park) and is open only during summer months, allowing a seasonal connection by road between Estes Park and Grand Lake. Berthoud Pass, at the headwaters of the Fraser south of Winter Park, connects the valley via U.S. Highway 40 to Interstate 70 in Clear Creek Canyon. This latter route is the most direct route between the valley and Denver.