To get to the first treasure map of the Ash Heap region, I fast travelled from my camp to the exterior of The Rusty Pick. Again, never undervalue saving a few caps — you'll regret not having those caps when you find a camp vendor with the Machete Sacrificial Blade plan going for 15,000 caps, and you just popped needed caps on a lazy fast travel!
Once you hit the Pick, fast travel to the AMS Testing Site located almost straight south of Murmrgh's place. You'll have to forgive my video directions — I was on the tail end of a Vintage Nukashine bar crawl when I filmed it. In any case, from the AMS Testing fast travel arrival point, head to the big yellow crane, spin in a slow circle, and you should see a culvert blocked by a rebar barrier. The treasure mound is right next to the left concrete embankment — about half way up the incline. It is hard to see, but you'll trip over it eventually. On my trip I got a bonus wendigo — maybe you'll get two!