Final answer:
In an area with significant extrusive igneous rock, one would expect to find evidence of volcanic activity, as this type of rock is formed from rapidly cooling lava on the Earth's surface.
Step-by-step explanation:
If a significant amount of extrusive igneous rock is found in an area, one would expect to also find volcanic activity in the area. This type of rock forms from magma that erupts onto the surface of the Earth and cools rapidly. Such evidence of volcanic activity might include lava flows, pyroclastic deposits, or volcanic landforms like cones and domes. It is less likely to find large mountains, deep valleys, or fossilized remains solely based on the presence of extrusive igneous rocks, as these phenomena are not directly associated with the process of extrusive rock formation.
In an area like the Central Andes Mountains, you find both intrusive and extrusive igneous rocks due to the long history of subduction-related volcanism and igneous activity. The extrusive igneous rocks are typically associated with the surface expressions of this volcanic activity, such as lava flows and ash deposits, whereas intrusive rocks are formed from magma that cools slowly beneath the surface. The differences in the map patterns of recent volcanoes, Neogene extrusives, and Neogene intrusives could be explained by the different timescales and processes involved in their formation.