I commuted for thirty years with a chrome-moly frame and was quite happy with that rig.  Durability is a very important characteristic.  You will have the occasional spill or accident' once about every seven years, if my experience is any guide.

Plan for panniers or frame packs.  You will have a fair amount of stuff to cart around - one reason why light weight is not critical in a commuting context

My career was in the NPS and fortunately, due to an emphasis on fitness, I had access to a shower and even a locker. i'll bet you will find the same in the USFS.  it really helps

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