My first guess would be winter burn, especially with the January we had this year. C. nootkatensis does not fare well with cold, dry conditions. In my opinion they are also a bit slow to root. Given the fact it had not much time to add fine roots the desiccation pressure may have done it in.
Look, too, for rodent damage where the trunk meets the ground as well. Those same winter conditions forced a lot of rodents into mulched areas with nothing to eat for a long time. Also beware of road salt, and chlorine from pool filter backflush.
My condolences.