1. Rio Nido, Sonoma County (OES Mission #98-CST7172). On 02/07 a large landslide failed along the Russian River at Canyon Three near Sweetwater Springs Road. The slide was a rotational failure near the ridgetop that split downslope into debris flows affecting houses at the base of two canyons. DMG concluded that deep tension cracks in the source area indicate additional material could fail, putting approximately 200 people at risk. Also, if material fails all at once, a landslide dam could form, causing flooding upstream. DMG provided information used by the county in the evacuation of residents and development of access (re-entry) plans; DMG also recommended monitoring of the slide and retention of a consulting engineering geologist to evaluate on-going conditions at the site. The preliminary report prepared by DMG geologist Wayne Haydon was released on 02/09 and the final report was released on 03/09. On 02/07 six houses slid down a hillside near the Russian River in Sonoma County; 300 other homes were evacuated (Siang Tan, DMG, 02/11). 240,000 cubic yards of earth were threatened by a landslide on 02/17 (Tan, 02/19).
3. Richmond, Contra Costa County (OES Mission #98-CST7204). On 02/10 DMG evaluated a cutslope failure, about 80 feet wide and extending about 60 feet south, above Wildcat Creek Road between Highway 80 and Richmond affecting access to about 25 homes. DMG determined there was no imminent danger to homes upslope from the failure and recommended the private landowners hire a consultant to design measures for de-watering the slide. A report prepared by DMG geologist Chris Wills was released 03/09.
5. Fitch Mountain, Sonoma County (OES Mission #98-CST7243). On 02/21 DMG evaluated a landslide affecting two homes on North Fitch Road near Healdsburg; 60 additional homes were originally thought to be in potential danger. DMG determined that a small slide on the north side of the mountain had liquefied at the toe and had moved downslope onto the road near the two houses; the road did not appear to be impacted by the slide plane. DMG recommended debris be periodically cleared from the road and behind barriers around the homes made from sand bags and K-rails, and that landowners hire a consultant for longer-term mitigation. A report prepared by DMG geologist Haydon was released 03/23.
9. Santa Cruz County overflight (OES Mission #98-CST7255). On 02/24 DMG participated with the OES, USGS and county staff in an overflight of approximately eight significant landslides and multiple others of concern to the county. One large landslide blocked Eureka Canyon isolating 500 local residents. Debris flow failures were observed in the northern part of county. Larger, deep-seated failures occurred in the mid and southern parts of the county; however, Eureka Canyon was not visible due to fog and bad weather. A report by DMG geologist Tom Spittler was released on 04/30. On 02/25 more than 50 homes were seriously damaged by debris flows and seven homes due to deep-seated landslides (Joe Hanna, Santa Cruz County geologist).
10. City of Napa, Napa County (OES Mission #98-CST7256). On 02/24 DMG reviewed three landslides impacting four homes and two county roads providing critical access to remote communities. On 03/11 DMG responded to an additional request to evaluate landsliding affecting a house along Sage Canyon Road and Highway 128, east of Lake Hennessey. A report by DMG geologist Manson was released 04/03.
11. City of Vallejo, Solano County (OES Mission #98-CST7263). On 02/10 DMG evaluated a large section of hillside overlooking the Sandy Beach area that developed a large crack and several smaller slides with potential to impact approximately 40 homes at the base of the hill. DMG determined that only two homes were likely to be affected by near-future movement of talus materials at the base of the slope. A report by DMG geologist Wills was released on 03/20.
12. City of San Bruno, San Mateo County (OES Mission # 98-CST7266). On 02/13 DMG received a request for assistance in evaluating numerous failures in San Mateo County. On 03/12 DMG evaluated debris flows that were undermining structures and public property in three areas that continue to experience debris flow movement, creep and slippage. The Crestmore Drive slide involves the backyards of homes on Crestmore Drive and Madison Avenue and a city-owned parcel. The Crestmore Canyon area includes several small slides which endanger houses or yards at the top of the surrounding slopes, with the potential to become larger and more damaging, similar to what has occurred at the Crestmore Drive slide. A report by DMG geologist Wills was released 04/08.
13. City of Fremont, Alameda County (OES Mission # 98-CST7267). On 04/07 DMG received a request to assist the City of Fremont with mapping and evaluation of the Mission Peak landslide. This is a large complex landslide, 1000 feet wide by 4000 feet long, with portions that might be several hundred feet deep, and 40 to 70 feet deep in the toe area. The apparent lower toe was uplifting one to 1.5 feet per day and moving four feet horizontally at the toe on 03/27. Properties on Grapevine Terrace, Rutherford Place, Rutherford Court, and possibly Vista Del Sol may be affected by the slide. The slide is too large to determine the immediate threat without evaluation. An initial report on the slide was prepared on 04/08 by DMG geologist John Schlosser who was assigned to this project under the direction of the city's consultant. A final report was released 05/20.
20. San Francisco, San Francisco County. On 01/20 a small car was caught in a huge sinkhole on John Muir Drive in San Francisco. Blocked sewers caused flooding, which caused the road to collapse. The latest storm caused widespread power outages, downed trees and flooded roads (Sacramento Bee). On 02/12 a slipping hillside was reported in San Francisco’s Sea Cliff neighborhood (Tan, 02/19). On 03/03 mudslides near Mt. Davidson (Mira Loma Park area) resulted from poor drainage of city pipes upslope from failures; a retaining wall constructed after 1995 and 1997 failures failed again (Pam Dickey, San Francisco resident). On 03/13 a Bay View Hill landslide occurred near Candlestick Park (USGS).
21. Oakland Hills, Alameda County. Between 02/02 and 02/07 three homes were affected by slides. In addition, numerous small slides blocked roads along the coast in both northern and southern California (Bedrossian, 02/05). On 02/25 a dramatic landslide in the Oakland Hills destroyed two homes. Seven homes were red-tagged, an additional seven homes were yellow-tagged, and 11 others were monitored for potential trouble (USGS, 02/26).
22. San Francisco Bay Area. Recent debris flows were observed in the eastern part of the region from Niles to Oakland. Deep-seated landslides in the area of Daly City to Moss Beach area moved (USGS, 02/25). A few newly initiated debris flows and several others reported earlier show signs of recent activity (USGS, 03/12).
23. Mill Valley, Marin County. On 02/02 two homes were affected by slides (Bedrossian, 02/05).
25. San Mateo County. On 02/03, the northern California storm was blamed for one death in San Mateo County (Tan, 02/11). On 02/10 a landslide on park lands threatened a home in Montara near Montara Beach (Len Miller, OES). On 03/03 Devil's slide failed along Highway 1 south of the 1995 failure (Channel 3 News). On 03/03 a landslide in San Mateo County threatened a 96-inch Hetch Hetchy pipe that provides water supply to San Francisco. San Francisco Water Department is monitoring the slide; the pipe may need to be relocated (USGS).
26. Bodega Bay, Sonoma County. On 02/05 high waves and wind-blown rains took a toll on the bluffs above Gleason’s Beach where, several homes were in danger of sliding into the surf. All of the residents were evacuated (The Davis Enterprise). On 02/11 heavy rains continued to trigger landslides in both northern and southern California. Numerous homes were impacted along the Sonoma County coastline at Gleason's Beach north of Bodega Bay and in Monte Rio (Bedrossian, 02/11).
29. Daly City, San Mateo County. On 02/06 unstable slopes threatened seven homes in Avalon Canyon (Tan, 02/11). On 02/12 a collapsing hillside in Daly City threatens sea front homes as continuing storms cause mudslides (Tan, 02/19).
35. San Benito County. On 02/11 DMG received a call from OES regarding the river jumping a channel and undercutting banks near a home (Bedrossian, 02/11).
40. Scotts Creek, Santa Cruz County. Many draws were blown out by debris flows, translational-rotational slides and slumps. Most of the debris appears to be from residual landslide deposits that moved during previous storms (Roberta Smith-Evernden, consultant, 02/17). On 03/03 DMG received a request from CDF to examine slides resulting from storms on a Timber Harvesting Plan (THP) previously reviewed by DMG. DMG examined erosion control measures implemented in the THP, particularly along a newly constructed road near Scott's Creek. One debris flow occurred in brush lands outside of the managed area and several old fills on existing roads had begun to crack and fail. DMG made several recommendations for additional drainage control measures along the road (Spittler, 03/10).
44. Davenport, Santa Cruz County. On 02/25 there were many debris flows, some affecting homes in the bottom of draws. Some failures were THP related, mostly in the northern part of the county. Mid-county larger slumps and translation-rotational slides occurred. Near Corralitas, very large old slides were reactivated (Spittler, 02/25).
46. Blucher Valley, Sonoma County. On 03/09 two houses were affected by the reactivation of the Blucher Valley landslide. The slide, which is located on very gentle (10 to 20 degrees) dip slopes of the Wilson Grove Formation, originally moved in 1983. DMG geologist Spittler visited the site on 03/09. Fractures were present down the face of the slide and the toe had migrated upslope 50 to 100 feet, i.e., the toe of the original failure in 1983 was acting as a buttress to present movement, causing the ground above the toe to buckle. Two houses on the toe were affected; one was yellow-tagged, one was red- tagged.
47. Russian River, Sonoma County. On 03/04 DMG received a request from CDF to examine slides resulting from storms on a THP previously reviewed by DMG. DMG examined two small landslide failures along roads within Little Whiskey Creek, a tributary drainage to the Russian River in Sonoma County. No sediment had reached the watercourses. DMG made recommendations for removal of debris from the roads and future stabilization of the slides (Spittler, 03/10).
48. La Honda, San Mateo County. On 02/19 in La Honda nine homes were threatened by a mudslide; three houses were red-tagged (Tan, 03/05). On 03/13 a large, slow-moving, deep-seated slump affected 25 homes. The main slide had been moving continually since 02/11, but recent rain accelerated movement. Three houses at the head of the slide were red-tagged and five other houses are on or adjacent to it. The slide appears to be enlarging in the downslope direction. USGS employees mapped the landslide to determine its relationship to another, smaller landslide downslope from it. San Mateo County drilled three wells in a road that crosses the slide and has been pumping the wells since 02/26. Trenches were also dug and lined with plastic to provide drainage. The county geologist plans to drill exploratory borings based on USGS input (USGS, 03/20).
49. Big Sur, Monterey County. On 03/13 landslides blocked Highway 1 at Hurricane Point, eight miles northwest of Big Sur (USGS).
52. Las Lomas, Monterey County. On 03/10 a slide moved toward Las Lomas Drive. The toe reached into the yards of three homes on Las Lomas Drive. Seven homes on the west side of Las Lomas Drive were considered for evacuation if sewers or other utilities were disrupted (USGS, 03/12). On 03/13 the Flora Drive slide continued to move, affecting 10 homes (USGS). On 03/19 the slide continued to move at a reduced rate. Houses on the slide held together; the two worst damaged homes were in the middle of Flora Drive. Access and utility problems continued (USGS, 03/20).
53. Cloverdale/Geysers Road, Sonoma County. A chronic earthflow showed renewed movement. The earthflow passes under an existing viaduct on Highway 101 between Cloverdale and Squaw Rock (USGS, 03/12). The Cloverdale/Geysers Road was closed due to landslide activity (Henderson, 03/13).
54. Sebastopol, Sonoma County. A landslide threatened three homes in a rural area two miles west of Sebastopol. The slide, which is roughly 1000 feet long by 200 feet wide, knocked one of the homes off its foundation. A second home slid down a hill and a third was heavily damaged (USGS, 02/26). On 04/21 DMG received an inquiry for historical information about a deep-seated translational landslide that affected several properties on Gold Ridge Road on 02/19. The slide occurred at the interface between the steep slopes below and flatter ground above under geologic conditions similar to the Blucher Valley landslide (see # 46, Spittler, 04/29).
57. Highway 80, Solano County. Throughout the 1997-98 season, a large-scale, deep-seated complex landslide on Highway 80 west of the Red Top exit continued to move slowly. The slide has disrupted Highway 80 and the nearby frontage road for several years possibly due to the undercutting of the toe by the stream channel below. The slide measures about 2000 feet wide and 3000 feet long with an estimated depth of approximately 100 to 150 feet. Significant cracking along the frontage road 1000 to 2000 feet southwest of the main landslide suggests activation of a new landslide in this area (Donn Ristau, consultant, 04/13).
58. Petaluma, Sonoma County. In December 1997 a slide disrupted Sonoma Mountain Road, east of Petaluma (north of the residence at 550 Sonoma Mountain Road). The failure appears to be the reactivation of an older, deep-seated slide complex that flanks the western boundary of the Rodgers Creek fault zone. The slide is approximately 400 feet in length and approximately 150 feet wide. The northeast lateral margin of the slide resulted in vertical displacement (down) of the road four feet. The vertical relief in the headscarp of the failure indicates the upper portion of the slide dropped approximately eight to ten feet. The depth of the failure is estimated to be at least 15 feet in the central portion of the slide mass (Ristau, 05/19).
59. Carmel Valley, Monterey County. In December 1997 a series of debris slides failed off the northern flank of Saddle Mountain in Carmel Valley and impacted the Saddle Mountain Recreation Area. Failures were typically 50 to 100 feet in length, 30 to 50 feet in width and three to six feet deep. The underlying bedrock is a massive sandstone and pebble conglomerate in which the weathered residual soils liquefied. Steeply dipping, out-of-slope fractures apparently resulted in the sloughing of weathered slabs of rock. In several areas the debris slides triggered the additional failure of outboard fill slopes (Ristau, 05/19).
60. Santa Rosa, Sonoma County. On 03/03 DMG was notified of the reactivation of the Lost Acres landslide that occurred in the Bennett Valley area of Santa Rosa during the winter storms of 1995 and 1997 (Norman Dolan, homeowner, 03/03). The Lost Acres landslide is a large, deep-seated rotational failure that covers about 12 acres and encompasses a hillside bench and flanking slopes of the adjacent drainages, beneath an east-north facing slope. Four residences were tagged for limited entry and one house was tagged for no entry in 1997 (Haydon, 03/05/97).
61. Pacifica, San Mateo County. Residents of seven homes were evacuated on Esplanade Drive on 02/22 as a result of sliding and erosion of the cliffs. During the previous two weeks, the 30 foot tall cliff retreated ten feet to the rear edge of the homes (USGS, 02/27). On 03/03 seacliff slumping affected several homes in Pacifica (Channel 3 News). Although the rate of cliff erosion, soil falls, and rock falls decreased, water was still seeping from the face. Material that failed was mainly a fluvial deposit on top of a marine terrace deposit. Seawall and other mitigative designs were being considered (USGS, 03/12).
62. Orinda, Contra Costa County. Three houses remained in precarious situations after a mudslide threw them off their foundations (USGS, 02/26).
63. San Leandro, Alameda County. A massive landslide threatened seven homes on Hillside Drive, including two that had to be moved off their foundations on 02/21 and 02/22 to save them from the encroaching wall of mud. The slide is about 90 feet high by 200 feet wide (Bill Cotton, consultant, 02/22). The San Leandro slide now has a volume of 65,000 to 70,000 cubic yards; it has moved a total of about five to six feet on a slope of 1.5 to 1. The slide is a translatory failure in decomposed and highly sheared gabbro near the Hayward fault. The subdivision was built in the late 1970's and early 1980's. Two homes were moved by the slide. The slide were mapped and inclinometers were positioned on the slide. Remedial measures were being planned (USGS, 03/11).
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