2. Clear Lake Oaks, Lake County (OES Mission #98-CST7200). On 02/10 DMG evaluated two houses in danger of collapsing onto Highway 20, five earthfilled dams, and two damaged roads in the vicinity of Clear Lake. DMG made recommendations regarding removal of one structure, installation of drainage measures on two others under direction of a consultant, drainage of two dams as proposed by Caltrans engineers, and monitoring and removal of debris from the road failures. The report prepared by DMG geologist Mike Manson was released on 03/09.
4. Morro Bay/Pismo Beach, San Luis Obispo County (OES Mission #98-SOU6106).
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a. Morro Bay. On 02/12 DMG evaluated reactivation of two landslides that failed in 1995. Approximately 25 houses were built on the toe of one slide, and 15 houses were adjacent to the toe of the other. An underground water pipeline crosses both landslides. DMG concluded that no immediate risk or emergency was evident, however, potential debris flow and earthflow activity could impact the road and several residences during intense rainfall of long duration. DMG recommended a consultant be retained to evaluate existing data, including monitoring and mitigation being conducted by upslope owners. A report prepared by DMG geologist Tan was released on 02/23. Reactivated landslides from 1995 storms affected 34 homes, with seven to eight damaged (USGS, 02/26).
b. Pismo Beach. On 02/12 five coastal bluff failures affecting city roads were evaluated by DMG for potential threat to pedestrians and residences. Increased sea wave erosion, surface water erosion and urban irrigation contributed to these failures. DMG discussed feasible mitigations with city engineers. A report prepared by Tan was released 03/09. |
7. Big Lagoon, Humboldt County (OES Mission #98-CST7235). On 02/16 DMG evaluated cliff erosion affecting three houses in the Big Lagoon area near Agate Beach, where high energy El Niño storms and seasonally high tides eroded the cliff face at an accelerated rate. The county yellow- and red-tagged several structures. DMG recommended retaining a licensed consultant with experience in coastal erosion to assist in developing formal tagging distances for existing residences. A report prepared by DMG geologist Jim Falls was released 03/23.
8. Weott, Humboldt County (OES Mission #98-CST7252). On 02/23 DMG evaluated two landslides along access roads to a sewer treatment facility and city water tank/repeater phone sites. DMG made recommendations as to repairs to be considered. A report prepared by DMG geologist Falls was released 03/12.
24. Highway 50, El Dorado County. Highway 50 was blocked for about 12 hours by a cutbank failure. The failure was about 50 feet wide and 25 feet high, of outer surface sloughing from pore water pressure. The failure was located just west of the active Whitehall landslide being monitored by USGS and Caltrans. The Cleveland Corral landslide continued to move and erosion occurred on the Mill Creek slide (Ken Cole, Caltrans). A landslide previously reported along Highway 50 between Twin Bridges and Sly Park was a snow avalanche (Wieczorek, USGS, 02/25).
36. Magalia, Butte County. On 02/11 DMG received a call from an individual in regard to a sinkhole that collapsed approximately 20 feet from a house (Bedrossian, 02/11). The sinkhole may be related to the collapse of an old mining shaft, but this has not been verified.
43. Ukiah, Mendocino County. On 02/25 a house was affected by a rotational slide below the house. The house was red tagged; 12 feet of movement occurred in two days in an area previously mapped as landslide by Robert Sydnor and Julie Bawcom for Mendocino County (Sydnor and Bawcom, DMG OFR 91-16). Four other houses were red tagged in the area mapped. Use of a consultant was recommended (Bawcom, DMG, 02/25).
45. Santa Maria, Santa Barbara County. A portion of the bank of the Cuyama River collapsed along Highway 166 13 miles east of Santa Maria, taking along a tractor-trailer rig and a half dozen cars, including a California Highway Patrol cruiser. Two people were reported killed (USGS, 02/26). On 02/24 flooding and mudflows caused collapse of Highway 166, killing two CHP patrolmen (Channel 3 News, 02/28).
50. Interstate 5, Lake Shasta, Shasta County. On 03/13 a fill failure along the shore of Lake Shasta closed the outside lane of Interstate 5 (USGS).
51. Highway 96, Siskiyou County. On 03/13 a debris flow with an estimated length of 1000 to 2000 feet blocked 2/3 of the channel of the Klamath River and covered several hundred feet of highway about 13 miles north of Humboldt County (USGS).
55. Grass Valley, Nevada County. On 05/08 DMG participated in a news briefing regarding the collapse of the Old Brunswick shaft of the Idaho-Marilyn Mine Complex near Grass Valley in the vicinity of new $400,000 homes (Bob Hill, DMG, 05/11).
56. Oroville, Butte County. On 04/23 DMG received a request for assistance from the Office of Mine Reclamation regarding a citizen in Oroville whose property was collapsing due to old mining tunnels. DMG geologist, Bob Hill visited the site and prepared a short report. DMG staff are researching historical mine activity to determine the extent of underground mine tunnels in the Oroville area. This appears to be an area-wide problem, not an isolated incident (Hill, 04/25).
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