Though not really a clue per se, I've always considered the original Waltz directions published by Bicknell in 1884, and also given by Northcutt Ely in 1953, as the most important primary information of all.
Northcutt Ely....
" Ruth had taken with him a metal box in which he kept the old Spanish map and various other documents, which described how to reach the mine. This box had been found in Ruth's camp. The map was missing. On the body itself, however, had been found a memorandum book, which Erwin Ruth showed me. It bore, in his father 's handwriting, in ink, directions which covered the last short distance to the mine.
It read as follows:
"It lies within an imaginary circle whose diameter is not more than five miles, and whose center is marked by the Weaver Needle, about 2,500 feet high, among a confusion of lesser peaks and mountainous masses of basaltic rock.
"The first gorge on the South side from the West end of the range -- they found a monumented trail which led them northward over a lofty ridge, thence downward past Sombrero Butte, into a long canyon running north, and finally to a tributary canyon very deep and rocky and densely wooded with a continuous thicket of scrub oak...
The description was broken off at this point, but lower down on the page, well spaced and standing by themselves, were the enigmatic words "veni, vidi, vici" and then, written in pencil below this, was the notation About 200 feet across from the cave ".
Bicknell.....