San Francisquito Creek is currently listed by the California State Water Resources Control Board as being impaired by sediment and by the organophosphate pesticide, diazinon. Water quality in the creek is of particular concern because the creek is habitat for steelhead trout, a federally - listed threatened species. This study reports results of water year 2010 stream gaging and water quality sampling conducted as part of the Long-Term Monitoring and Assessment Program (LTMAP), a surface-water monitoring program sponsored by Stanford University and the City of Palo Alto. Water year 2010 was the ninth year of monitoring at the Los Trancos Creek and San Francisquito Creek stations at Piers Lane, and the seventh year of monitoring at the Bear Creek at Sand Hill Road station. Due to budget constraints, only flow and sediment were monitored at Bear Creek beginning in water year 2007, and at the Piers Lane stations beginning in water year 2008. Measurements and observations at all three stations are continuing during water year 2011, though on a limited scale. Since fall 2001, Balance Hydrologics, Inc. has operated for LTMAP two automated water -quality sampling stations on San Francisquito Creek and Los Trancos Creek at Piers Lane, just above their confluence. In fall 2003, Kinnetic Labs (Santa Cruz) installed another automated sampling station, located on Bear Creek at Sand Hill Road, along the northern border of the Jasper Ridge Biological Preserve. The station, which is now also operated by Balance Hydrologics, is configured similarly to the other stations with a datalogger, several p robes, and a programmable pumping unit. As in previous years, the electronic records were combined with manual measurements to create flow records for each stream. Measurements of temperature, specific conductance, dissolved oxygen and pH were made manually. Suspended-sediment samples were collected as grab samples during and between storms and used to estimate annual suspended-sediment yields. Our conclusions are p resented below, together with citations to the relevant text subsections, tables and figures: 1. Rainfall and streamflow totals for water year 2010 were slightly above average. Rainfall at the Bear Creek station was approximately 115 to 128 percent of the longterm average. Due to brief periods of gauge malfunction, the rainfall record at Piers Lane was partially based on correlation to nearby rainfall stations, and was estimated at 112 to 133 percent of the long-term average. Peak streamflow was slightly above average; based on USGS provisional streamflow data for San Francisquito Creek, the peak flow for the year corresponds to about a 4.1-year recurrence-interval flood, equivalent to a 25 percent chance of being exceeded in any year. (Sections 4.1 to 4.3; Table 4; Figures 2 to 5) 2. Specific conductance values (Section 6.1; Tables 1 to 3; Figures 8 to 10) and pH values (Section 6.3; Tables 1 to 3; Figure 14) in all three streams were within the range of previous sampling results during water year 2010. 3. Dissolved oxygen concentrations (Section 6.4; Tables 1 to 3; Figures 15 to 17) were occasionally low-particularly in San Francisquito Creek in late summer or fall-a condition which may p rove limiting for certain biota. This is consistent with previous years. 4. Dry-season water temperatures remained below lethal levels and below temperatures recorded in 2006 and other years, despite low baseflows and discontinuous pools in some upstream reaches in fall 2009. Low baseflows have a higher potential for high stream temperatures and, therefore, a greater impact on steelhead and other aquatic biota, especially if pools become discontinuous (Sections 4.4 and 6.2; Tables 1 to 3; Figures 11 to 13). 5. Fluctuations in flow and specific conductance during baseflow periods were most noticeable at the Bear Creek station, but also propagated downstream to San Francisquito Creek at Piers Lane. In addition, our records show multiple and various types of flow alterations in Los Trancos Creek. Upstream diversions and other flow alterations may affect baseflows and, therefore, aquatic habitat. Besides the volumetric changes to flow, water quality may also be altered by additions to creek flow (Section 4.4; Figures 3, 6, and 11 to 13). 6. Even though water year 2010 was slightly above average in terms of total flow and peak flows were moderately large, roughly average or slightly below-average amounts of sediment were discharged (Section 6.5.3; Table 4).