This sounds like Bishop, not Mammoth. Bishop is 30 minutes outside of Mammoth and is a little bit bigger. Mammoth does have two grocery stores now, for years it was just a Vons and now there is a Grocery Outlet as well.
Bishop has a Vons, Grocery Outlet, and a Smart and Final. Both cities have some hispanic grocers that I'm not familiar with. As far as I know though there has never been a K-Mart in Mammoth, and I've snowboarded there since ~2002.
Bishop did used to have a K-Mart and it is just sitting empty now.