Index map showing location of selected lake and stream sites in the Mount Shasta area 2. Map showing location of wells and springs and measuring sites on streams and lakes 3. Hydrograph of well 40N/2W-25L1, August 1981 through August 1982 4. Hydrograph of well 41N/5W-26L1, August 1981 through August 1982 5. Bar graph showing mean monthly temperatures of water from well 42N/4W-18D1 during 1982 6. Hydrograph of flows at temporary continuous-recording gage Mud Creek at Road 13, near McCloud 7. Hydrographs of flows at temporary continuous-recording gage Whitney Creek at Highway 97, near Weed Water year, as used in this report, includes the 12-month period from October 1 through September 30. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 months.
A water-resources appraisal of the Mount Shasta area in northern California was completed to document present hydrologic characteristics so that comparisons could be made of possible future changes due to land use or volcanic activity. Data collected during this study include glacial areas and volumes, streamflow, sediment concentrations, temperature, and water chemistry of the ground water and springs. The lower flanks of Mount Shasta consist of broad, smooth aprons of pyroclastic-flow, debris-flow, and fluvial deposits. Incised channels on upper parts of the mountain tend to terminate on the flanks. Only four streams Mud, Whitney, Squaw Valley, and Ash Creeks have sufficient streamflow to reach downstream main channels or to travel more than about 6 miles from the summit. The difference in low flows of the various streams is attributed to variations in glacial melt, storage of ground water in the materials that compose the mountain and the alluvial fans, and the rain-shadow effect of the mountain on precipitation. Annual precipitation in the vicinity of McCloud, southeast of the summit, is about 53 inches, whereas on the northwest side, it is about 18 inches. Although Mount Shasta is an old volcano, lava flows and other volcanic activity have occurred within the last 10,000 years. The most recent of Mount Shasta's summit vents is Hotlum Cone, which may have erupted as recently as 200 years ago. Many springs issue from fracture joints in lava and lava tubes around the mountain; the main groundwater movement is generally away from the slopes of Mount Shasta. Where groundwater data were available, the direction of movement is in a downslope direction from areas of recharge near Black Butte and Mount Shasta to areas of discharge near Weed and Mount Shasta (city).
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