This is perhaps the most important exploration tool, but is often hampered by soil and vegetation cover, which effectively hides the underlying rocks. Where rock is exposed it is called outcrop. Outcrops provide vital information about potential ore-bearing host rocks, together with alteration and mineralization deposited by hydrothermal fluids, and the geological context of all these together. In the Cordillera del Condor, outcrops are rare and are generally limited to stream bed exposures and ridge tops; this means that other methods such as geochemical sampling of soils and geophysics are critical in locating potentially mineralized zones. In the Cajamarca region, outcrop is generally abundant and mineralization can usually be directly sampled. However, low-lying areas are often buried in river or glacial gravels, and some high-standing ground has recent barren volcanic rock covering potentially mineralized areas.