This study assesses a 60 km NNE-SSW transect along the San Gabriel River for shallow shear velocities, in San Gabriel Valley and the Los Angeles Basin of southern California. We assessed a total of 214 sites, 199 along the transect at 300 m spacing, during a one-week field campaign with the refraction microtremor (ReMi) technique. The transect's maximum 30-meter shear velocity (V s 30) occurs in coarse alluvium of San Gabriel Valley where the San Gabriel River exits the San Gabriel Mts.; at 730 m/s, upper NEHRP site class C. Much of the northeast section of the transect (in San Gabriel Valley) is also NEHRP class C, or near the CD class boundary. The section of the transect south from Whittier Narrows to Seal Beach shows NEHRP-D velocities in active alluvium. The transect's lowest V s 30 , 230 m/s at the Alamitos Bay estuary, is also classed as NEHRP-D. An increase toward the NEHRP CD class boundary occurs at the shoreline beach outside Alamitos Bay, confirmed by additional measurements on Seal Beach. Our measured V s 30 values generally show good correlation with published site-classification maps and existing borehole data sets. There is no evidence in our data for an increase in velocity predicted by Wills et al. (2000) at their "CD" to "BC" site classification boundary at the San Gabriel Mountains front, nor for any decrease at their "D" to "DE" class boundary at Alamitos Bay. Very large V s 30 variations exist in soil and geologic units sampled by our survey. The V s 30 variations we measured are smaller than V s 30 variations of 30% or more we found between closely spaced (<0.5 km) downhole measurements in the Los Angeles Basin, which are not uncommon within a community data set we examined showing hundreds of boreholes. We find the San Gabriel River's hydraulic gradient to be a good predictor of minimum V s 30 , based on the expected effect of the hydraulic gradient on the grain size of sediments deposited by a river. The V s 30 data show a fractal spatial dependence, which appears at distances greater than 700 m. The unprecedented number of shearvelocity measurements we have made suggests that large measurement populations may be necessary to properly characterize V s 30 trends within any surficial geological unit.

A 30‐month study of the comparative dynamics of the fish populations inhabiting Kelsey Creek, located in the City of Bellevue, Washington, and a nearby pristine control stream suggest that urban development has resulted in a restructuring of the fish community. Environmental perturbations, including habitat alteration, increased nutrient loading, and degradation of the intragravel environment appeared to have a greater impact on coho salmon Oncorhynchus kisutch and nonsalmonid fish species than on cutthroat trout Salmo clarki. Although the total biomass (g/m2) of fish in each stream was similar, its composition differed markedly. Ages 0 and I cutthroat trout were the majority of the fish community inhabiting Kelsey Creek, whereas the control stream supported a diverse assemblage of salmonids of various ages and numerous nonsalmonids. The rapid growth and greater biomass of salmonids in Kelsey Creek (a 2‐year mean of 3.51 g/m2 versus 2.03 g/m2 in the control stream) resulted in a total annual net production of these species of 1.6 to 3.3 times that of the control stream (a 2‐year mean of 7.6 g/m2 versus 3.5 g/m2 in the control stream). Marking and outmigrant studies indicated that environmental disruptions in the urban stream do not result in the displacement of the salmonid inhabitants.

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In October and November 2001, we performed an urban shear-wave velocity transect across 16 km of the Reno, Nevada, area basin. Using the refraction microtremor method of Louie (2001) we determined shear-wave velocity versus depth profiles at 55 locations. Shear-wave velocity averaged to 30 m depth (Vs30) is one predictor of earthquake ground-motion amplification in similar alluvium-filled basins, and it is the basis of site hazard classification under National Earthquake Hazards Reduction Program-Uniform Building Code (NEHRP-UBC) provisions. A geologic map-based NEHRP classification along nearly all of our transect line would be NEHRP-D, but our measurements of Vs30 revealed that 82% of the transect is classified NEHRP-C. Relatively stiff Tertiary sediments underlie the surface of the Reno basin, and weaker soils occur east of downtown Reno in the floodplain of the Truckee River. Although 53 of our locations were on the geologically youngest and most active fluvial units, these sites showed Vs30 values ranging from 286 m/sec (NEHRP-D) to 849 m/sec (NEHRP-B). Mapped geologic and soil units are not accurate predictors of Vs30 measurements in this urban area. A test model based on gravity results showed Quaternary-alluvium depth can be combined with transect Vs30 measurements to predict Vs30 across the Reno basin.

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