Salt marshes typically sit above the high tide mark true or false

This is false. They are not located above the high tide mark but rather in the intertidal area, which is the area between the land and the salt water and is constantly covered by tides. When the tides retreat, they leave the salt on the ground so salt water marshes are created in these areas, and they get tide flooded over and over again.

They both determine the exact age of rocks.