The thing with the streaks is that they come in different colors and that it is a long process.

The black streaks on the canyon walls in Zion National Park are primarily due to a geological process called desert varnish. This occurs when water, clay, microbes, and minerals interact over long periods, leading to the formation of a dark coating on the rock surfaces. Specifically, the black color is often attributed to the oxidation of manganese and iron oxides, which are carried by water seeping over the rock.