A groundwater-flow model was developed to contribute to an improved understanding of water resources in the Chambers-Clover Creek Watershed. The model covers an area of about 491 square miles in western Pierce County, Washington, and is bounded to the northeast by the Puyallup River valley, to the southwest by the Nisqually River valley, and extends northwest to Puget Sound, and southeast to Tanwax Creek. The Puyallup and Nisqually Rivers occupy large, relatively flat alluvial valleys that are separated by a broad, poorly drained, upland area that covers most of the model area. Chambers and Clover Creeks drain much of the central uplands and flow westward to Puget Sound. The model area is underlain by a northwest-thickening sequence of unconsolidated glacial (till and outwash) and interglacial (fluvial and lacustrine) deposits. Ten unconsolidated hydrogeologic units in the model area form the basis of the groundwater-flow model.