FS!
I think the only reason South Dakota doesn't celebrate Columbus Day is that they have zero Italian-Americans and a decent Native American population. Most people in South Dakota doesn't exactly love Native Americans. Sioux people are seen as the primary poor, uneducated non-white minority of the state who are generally shiftless, lazy, drunk, violent, etc.
That's not to say South Dakota is some horrible, racist place. It's nicer than one would expect, especially the Black Hills and Sioux Falls. I just wouldn't point to South Dakota as the paragon of caring about Native Americans.
It's not perfect. The situation of the Native Americans is unfortunate, and some Republican state officials have worked to suppress their mostly Democratic vote.
Having said that, we do not have the virulent racism against Native Americans that is remotely similar to the anti-black racism of the South. The situation on the reservations is shameful, but the federal government shares much of the responsibility for that. Native Americans throughout the country have been persecuted, but the fact that South Dakota is so far the only state that has replaced Columbus Day with Native American Day alone is a sign that we can do the right thing. Also, our own Tim Johnson is one of the greatest Native American friends ever to have served in the Senate.