My view of the poem:
First four lines: No clues just Forrest asking himself where he should hide his treasure
Begin it where warm waters halt: As discussed by everyone this is the hardest clue to decipher because it ultimately is your starting point. My view is that he is referencing warm water rivers and streams in New Mexico. So you would want to look for the highest elevation where you find a warm water river. This location would need to be at the entrance to a high elevation mountain canyon.
And take it in the canyon down: You wold follow the road into the canyon, and this road follow the floor of the canyon, and not be at the top or lip. Again, this canyon would be above the elevation of the warm water river or stream you started at.
Not far, but too far too walk: This is letting the reader know you should be in a car and expect a drive of a little distance. My guess is something over 10 miles, not more than 30-50 miles.
Put in below the home of Brown: I feel this is a reference to a location where you could fish for Brown Trout. I believe this because of the phrase “put in” a boating reference, and the word below, which you use when discussing locations along rivers and streams. I think you would be parking your vehicle downstream from the fishing location for the trout.
From there it’s no place for the meek: I think this is a reference to let you know the hike will be a little tiring for some. My idea is that you will be walking uphill and from my experience hiking at elevation is always a little taxing on me and my kids.
The end is ever drawing nigh: Fairly straightforward, you are close so don’t expect to be walking too terribly long.
There’ll be no paddle up your creek: This one references the fact that there will be a creek close by. The first bit of information lets you know you will be walking against the stream and it means you will not be following the creek because of the next line
Just heavy loads and water high:
Here in Oregon we have large number of logging roads in our federal and state forests. So if you take the two sentences together it is saying there will be a creek close by, but follow the logging road instead. Also, these logging roads here in Oregon all have gates to keep private vehicles off of them, I am not sure if they do that out there in New Mexico, but they do it a lot here. So the road represents the heavy loads(logging truck cargos) and the fact it is close to the creek represents high water. Logging roads here follow creeks as they wind through the mountains, but during high rains or spring melt off, the creeks crest their banks and the roads become impassable because of high water. So maybe Forrest is saying that the road could take heavy loads (log trucks) or be covered in high water under the right conditions.
If you’ve been wise and found the blaze- Straight forward hiking reference to marking your trail. From white marks on trees to barking them. Could be a mark on rocks also but it is a hiking reference.
Look quickly down, your quest to cease: My feeling is that because of the elevation you will be close to slope and he is saying look down over.
But tarry scant with marvel gaze- Don’t just wait and marvel at the beautiful view you see but get moving down the slope. Again, I believe the blaze will be at a point where you would want to just take in the incredible view if you were on a normal hike. Again, I believe the best vistas I have ever seen have been at elevation.
Just take the chest and go in peace- The chest should be visible from this location. Personally, I think he left in the open on the slope, but not too far down because of his age and agility when he took it there..
The next four lines I don’t feel are clues, but more a statement to the reader. Basically saying he knows why he has done it, and that it has tired him out. Also could be a reference to his age.
The last stanza has two more clues which I think are very important to identifying if you are looking in the right area
So hear me all and listen good- No clue
Your effort will be worth the cold- I believe this is a reference to the cold at elevation. I have hiked a lot of the Cascades and I can say that at elevation it is always cool, and as early as fall can be downright cold. I do not believe it is a reference to being in a cold water stream, rather that you are high up and it is cold up there.
If you are brave and in the wood- I believe this is Forrest telling the reader you must be in a forest to find this treasure. So you that is why I think you must be at elevation and in a forest.
I give you title to the gold: If you are cold and in the forest you get the gold.
I know that the starting point is the key, but Forrest has also said to move with confidence. So I think it is reasonable to use what I have said to look at map and cross reference to see if there are locations to fit what I have said. You know New Mexico much better than I do, and you would know if any of what I have said makes sense or is plausible. I will never be able to be there around Santa Fe to look for myself, but you have put in a lot of effort and if any of this helps, more power to you. Also, a lot of the logging roads may not appear on maps so you have to have knowledge of the area and which areas had been logged in the past.
I am not very creative and just thought I would take this poem as a straight forward, although vague, attempt at a treasure map. My Dad was a fighter pilot like Forrest and he was always fairly direct. So I think a straight forward simple approach would probably be best, and Forrest’s actual intent. Just my humble opinion.
Good luck and stay safe on your travels.