Triangular shaped deposits at cliff edges are termed alluvial fans. Alluvial fans typically form in arid regions were water flow is limited, so deposits of material are not washed away. Formation of these alluvial fans in the channel of Kasei Valles likely happened after any flow of fluid in the Valles system.
Orbit Number: 54132 Latitude: 23.0851 Longitude: 291.525 Instrument: VIS Captured: 2014-02-26 02:28
Photo credit: NASA/JPL-Caltech/Arizona State University