Pap
The petroglyphs were made by pecking into the sandstone. I think they may have used antler, and/or harder rock like chert. They used the chert to make arrowheads, spear points and other sharp cutting tools.
Many times they did their artwork on walls that had the dark patina and that were protected from the elements.
Since they are in sheltered locations, the have lasted a long time
Peter
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Peter Kaufman
NRA Life
GOA
SAF
RKCC CM-023
RKS #5642
SHAG # 005
Ironwood Nut
Life is too short to have ugly knives