The Pack River is a medium-sized river located in Northern Idaho. It is about long and drains a high mountainous area of the Idaho Panhandle's Rocky Mountains and Selkirk Mountains. The river flows into Lake Pend Oreille and is part of the Columbia River watershed via the Pend Oreille River. Course Its headwaters originate in the Selkirk Mountains, and flow in a southerly direction to the river's mouth at the northern tip of Lake Pend Oreille. It is the second largest tributary to the lake, after the Clark Fork River. Watershed The Pack River basin drains approximately . Watershed elevation ranges from a high of to a low point of at the lake, with a basin-wide average elevation of 3,730 ft. The upper portion of the watershed is mostly forested, and managed by the U.S. Forest Service. The lower watershed is under mixed public and private ownership, and supports a variety of uses. Mean annual precipitation in the basin is , much of which falls as winter snow in the mountains. Mean annual river flow at a mid-river gage is , with the highest mean monthly flows occurring in May (939 ft³/s) and the lowest mean monthly flow in September (54.7 ft³/s). Peak river flows for a 100-year event exceed . Pack River and its tributaries often experience more than one run-off event per year. Mid-winter rain-on-snow events can result in rapid snow melt, and in some years the peak flow from tributary watersheds occurs during these events. Following the Sundance wildfire in 1967, removal of the forest canopy was hypothesized to have produced an increase in annual stream flow from the basin and an advance of the peak flows by virtue of decreased transpiration losses and earlier snowmelt runoff generation. Tributaries The Pack River has about 34 tributaries. Grouse Creek is the biggest, followed by Rapid Lightning Creek, Jeru Creek, and Hellroaring Creek. These along with the West Branch of the Pack River are the crucial streams forming the River's size. Geology The underlying geology in the Pack River watershed is largely granitic, which decomposes into fine particles. Glaciation in the Pack River valley formed ice dams upstream of the confluence of many tributaries, resulting in large deposits of glacial till. Fine sandy sediments deposited in the dammed water are known as glacial fluvial deposits. These sandy areas today appear on mountain side slopes, forming very erosive soils. Because