which river's source place is portola valley and mouth in corte madera creek ?
SELECT DISTINCT var_uri where brack_open var_uri dbo_sourcePlace dbr_Portola_Valley,_California sep_dot var_uri dbo_riverMouth dbr_Corte_Madera_Creek_ attr_open San_Mateo_County,_California attr_close sep_dot var_uri a dbo_River brack_close