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Fig. 1. (a) Map of the Johnson Creek watershed, Portland, OR, USA. Solid squares indicate sample sites within urban land use areas, while solid circles indicate sample sites in nonurban areas. (b) The shaded area indicates Troutdale Gravel aquifer (TG), while the nonshaded area indicates Unconsolidated Sedimentary aquifer (US) at surface level. The thick line indicates location of urban growth boundary (UGB); west of the UGB are urban land use areas, while east of the UGB are nonurban land use areas. RM = river miles from the mouth of the stream.
