It's (relatively) common knowledge that Mars is known as the "Red Planet" because of an abundance of iron oxide, AKA rust, on its surface. At first glance, that looks like "iron, iron, everywhere." But of course that's just the surface.
How common is iron in general on Mars? For example, if colonists wanted to produce iron, how long would it be before they'd have to start specifically digging mines to get at more? How easy would it be to refine iron from known surface substances on Mars, and how much iron you could reasonably expect to obtain thereby?