How did geologists decide where one division of the geologic time scale ends and the next begins

The difference(s) between the grand canyon and valles marineris is/are: (a) the grand canyon was formed by water, but valles marineris was not. (a) valles marineris is much longer than the grand canyon. (c) valles marineris is much wider than the grand canyon. (d) valles marineris has large volcanoes near it. all of the above

Does water only take one path through the water cycle? (15 points)

What kind of fault is the san andreas fault