Correspondence, memoranda, engineering notes, reports, logs, photographs, blueprints, maps, and accounting notes relating to the construction of the Tolt River Dam. Construction correspondence is arranged chronologically and includes a rudimentary index.

Reports and studies concerning Seattle's water supply, especially relating to the Tolt River Watershed. Includes geologic reports, foundation condition, design studies, and a history of the Tolt River. Also included is correspondence related to various studies.