The native american DNA samples are mostly collected from South American tribes which generally indicate mesoamerican. The gedmatch calculators will indicate what ethnicities your DNA is similar to, but does not indicate actual tribal descent or relationship. Miwok, by the way, is a tribe in California -- I have found it very easy to google for "miwok people" or "costanoan people" to find out more about some of the groups that come up in these lists.