Most likely, SpaceX’s proposed boring sites are for proof of concept rather than for colonization. At these sites there may be relatively easy access to water, a test that SpaceX is eager to perform, and if all goes well then they may intend for their first lander to refuel and return to Earth. A test of this sort would go a long way toward confirming the basic strategy for Mars Colonization.

As with Project Apollo, Dave Scott’s project, it is probably best to start with the safer places and work up to the grandeur.

There’s also Dave Scott’s famous “grandeur” argument. SpaceX’s proposed sites look boring in comparison.

https://www.nasa.gov/sites/default/files/atoms/files/e-melas-ez.pdf

” Our perchlorate brine electrolyzer operating under simulated Martian surface conditions produces >25× the amount of oxygen produced by the Mars Oxygen In-Situ Resource Utilization Experiment from NASA’s Mars 2020 mission for the same input power. Furthermore, our perchlorate brine electrolyzers are more efficient than state-of-the-art alkaline water electrolyzers under terrestrial conditions, providing a pathway to utilize suboptimal input feeds to produce ultrapure hydrogen and oxygen.”

Greg the Geologist. In a word, no. See this post:

SpaceX narrows Mars landing site for Starship to four prime locations

All those locations are in the northern lowland plans, which is flat, safe to land at, and has ample water very very close to the surface.

Landing in Valles Marineris will not be easy. The canyon floor is very rough, with a lot of sand dunes. It also traps you, making exploration elsewhere difficult. I think this is not a first choice, though it will definitely be looked at by the first settlers.