Detail view of a wall of the current arroyo. Here the river previously cut an arroyo into the sandstone (the blocks just below the man's hand) in a different path from the current one, depositing fist- to head-sized cobbles. That arroyo was then filled with fine-grained sediments prior to incision of the current arroyo.
The wall of this arroyo displays a small channel that was refilled prior to incision of the current arroyo (the old channel is where the layers of sediment appear to "sag" on the arroyo wall). Scientists can often find pieces of charcoal in these earlier channels (charcoal is the result of lighting-ignited wildfires) and use carbon-14 age determinations to gauge the history of incision and refilling at each site. The horizontal structure at the top of the channel fill indicates episodic deposition of fine-grained water-borne sediments. Episodic deposition was provided either by a series of low peak flows in this channel or by overflow from another channel. In either case, this channel was eventually abandoned in favor of another; such shifts occur frequently in sediment-laden streams.