Rock glaciers are distinctive geomorphological landforms, consisting either of angular rock debris frozen in ice, former "true" glaciers overlain by a layer of talus, or something in between. Rock glaciers may extend outward and downslope from talus cones, glaciers or terminal moraines of glaciers. There are two types of rock glaciers: periglacial glaciers, or talus-derived glaciers, and glacial rock glaciers, such as the Timpanogos Glacier in Utah, which are often found in the former places of glaciers. Possible Martian rock glacier features have been identified by the Mars Orbiter spacecraft. A rock glacier, especially if its origin is unclear, can be considered as a discrete debris accumulation.