On this site, we prefer not to use the word colonization, as that term can have negative connotations to some cultures on Earth. A future Mars community would likely need to depend heavily on local Red Planet resources, such as near-surface water-ice for its survival. The hydrogen and oxygen in water could be separated--oxygen could be used for breathing air or for creating an oxidizer in a fuel system. The carbon-dioxide atmosphere could also be used as a potential means of generating oxygen and/or fuel. Mars orbiters are looking at the surface to detect the chemical elements and minerals of which the Martian surface is composed. Perhaps the iron-rich "soil" (regolith) could be used as a raw material, along with other elements and minerals. It may sound simple, but the dirt on Mars is also probably key for creating shelters that would shield against the radiation levels on Mars, which could impact human health. Basically, the more resources we can find on Mars, the less we have to take with us when we go someday in the future. Careful resource use and recycling will also be key for sustainable habitats for humans, whether for short periods or for potential long-term communities.