<P> Large modern orogenies often lie on the margins of present - day continents; the Alleghenian (Appalachian), Laramide, and Andean orogenies exemplify this in the Americas . Older inactive orogenies, such as the Algoman, Penokean and Antler, are represented by deformed rocks and sedimentary basins further inland . </P> <P> Areas that are rifting apart, such as mid-ocean ridges and the East African Rift, have mountains due to thermal buoyancy related to the hot mantle underneath them; this thermal buoyancy is known as dynamic topography . In strike - slip orogens, such as the San Andreas Fault, restraining bends result in regions of localized crustal shortening and mountain building without a plate - margin - wide orogeny . Hotspot volcanism results in the formation of isolated mountains and mountain chains that are not necessarily on tectonic - plate boundaries . </P> <P> Regions can also experience uplift as a result of delamination of the lithosphere, in which an unstable portion of cold lithospheric root drips down into the mantle, decreasing the density of the lithosphere and causing buoyant uplift . An example is the Sierra Nevada in California . This range of fault - block mountains experienced renewed uplift after a delamination of the lithosphere beneath them . </P> <P> Finally, uplift and erosion related to epeirogenesis (large - scale vertical motions of portions of continents without much associated folding, metamorphism, or deformation) can create local topographic highs . </P>

What kind of rocks characterize the first phase of the cordilleran orogeny