More janis Joplin stamps, one page inside.

Letter 1:
Front of envelope
Stamps
Letter

This may be completely off base, but my first thought upon looking at this was that it looked almost like a map, 
and since this is Tucson it especially made me think of washes. I looked up a map of the washes in Tucson and 
they all are similarly situated and numbered. The small picture of the brain has the area that corresponds to
area 11 colored red. The 11 wash in Tucson happens to be north of Tucson, out in the Catalinas. A bit 
interesting as some of the clues have pointed to some "treasure" or item being lost of buried out in 
the mountains. FWIW

I was able to find what may be the original image used in the letter: http://www.pavillon-orange.org/blog/comment-fait-notre-cerveau-pour-sadapter-a-une-situation-inconnue-et-complexe/

It looks unaltered
	

	
The small bottom left brain is from a macaque monkey and an article https://neurosciencenews.com/executive-function-orbitofrontal-cortex-1506/  on the the 
"role of a specific brain region in deciding between conflicting options"