Alluvial fan could be the answer. Alluvial fans are cone shaped deposits of sedimentary particles. The particles can be sand. silt, gravel or clay. These land-forms are formed at the mouth of canyons or in valleys where ephemeral streams can occasionally transport material to the mouth of the canyons. An ephemeral stream is one that is created after a shower of rain or other form of precipitation; they are not permanent streams. <span />
