The relative influence of landscape vs local processes on variation in stream C and energy sources to lotic consumers remains unresolved, but is a key component in understanding pathways through stream food webs. I investigated potential linkages between the distribution of δ¹³C signatures of primary producers (periphyton), terrestrial organic matter (detritus), and secondary consumers (aquatic invertebrates and fish) and: 1) drainage area and 2) stream reach geomorphology in 3 mountain watersheds of northern Idaho, USA. When considered alone, drainage area explained variation in the δ¹³C signatures of periphyton (R²  =  0.30) and sculpin (R²  =  0.15) only. Subsequent General Linear Models (GLMs) showed that stream morphology explained significant variation in δ¹³C of periphyton (79%), Diptera (93%), sculpin (51%), and trout (63%). Drainage area was not significant in these models, a result indicating that once δ¹³C signatures are explained as a function of geomorphic type, the contribution of drainage area becomes less important. On the whole, consumer δ¹³C signatures related more strongly to periphyton δ¹³C than detrital δ¹³C, though this relationship varied among geomorphic types. Collectively, results indicate that the morphology of a stream reach (including factors such as substrate size and storage elements, floodplain development, etc.) may be an important factor in the assimilation and distribution of C in food webs in forested mountain streams.