The nature of soils will vary with topography, which can be understood by comparing the thin rocky soils of mountain tops to the thick fertile soils of grass-covered lowlands. Even in a featureless lowland, the nature of a soil will vary greatly depending on whether or not it is well drained; although the drainage of soil is not completely independent because vegetation, microclimate, and the age of the land surfaces will vary within a given landscape. However, in smaller areas, the limiting factors may be so extensive that a variation in soils across a landscape will constitute a true toposequence (topographical sequence), and the features within these soils can yield reliable topofunctions (topographic functions). Bold landscapes like alpine ridges and peaks can be resolved based on distinct slope-related processes. For example, steep alpine slopes have sparse vegetation with soils that are eroded by snow melt, agitated by frost heave, and impacted by rock fall. These processes create thin, shallowly rooted, lightly weathered and rocky soils that are indicative of a mountain slope environment. The size and degree of these processes do not allow for strict analysis as topofunctions because of the extensive variation in climate, vegetation, parent materials, and land surface age at different elevations on a mountainside. (Retallack 2001)