Because weathering is an ongoing process, steep mountain slopes are constantly wasting away, often in the form of rocks falling and bouncing down slopes. Such falls can be triggered by freezing of water, the growth of plants (and their roots), earthquakes, or by people hiking on the slope. Rock falls occur in just a matter of seconds, so they are difficult (though fun) to observe. But, you can tell where rock falls occur on a mountain slope by looking for talus, a buildup of loose, angular rocks at the base of a steep slope.