Ethnohistorical sources regarding the creation of rock art around the world frequently make reference to "little people" as the makers of rock art.
As David Whitley (1991) has noted, this may be due to a taboo against talking
about a dead shaman and not verbally distinguishing the shaman's spirit
helper or tutelary spirit from the deceased shaman.
My ethnohistorical research with the Native American Ojibwa in northern
Minnesota and elsewhere in the midwestern United States, indicates that
Spreading Dogbane (part of the Periwinkle family), Catnip, and Deadly Nightshade
were used by the Ojibwa shamans (who made the rock art) as hallucinogens.
In researching atropine hallucinations (e.g. from Deadly Nightshade,
a dangerous poison), I discovered a medical literature that indicates that
people who take atropine hallucinogens and people in the second stage of
alcohol withdrawal during delirium tremens (i.e. they have stopped drinking
two to three days earlier) often see "little people" for half an hour.
Apparently Harner in the 1970's concluded that atropine hallucinogens were
responsible for stories of European witches "flying" and may be responsible
for the stories of lycanthropy, or people turning into animals.
As odd as this sounds, I would suggest that the effects of atropine
and alcohol may account for the numerous reports of "little people"
making rock art around the world.
Loud sounds often trigger the synesthesia that occurs in the later
stages of altered states (such as banging a rock) and can result in the
blending of foreground and background. This distortion of perception is
commonly used in filmmaking to create the "lilliputian" illusion.
A similar lilliputian illusion would result from the use of atropine hallucinogens by the shamans who made the rock art to record their vision experiences.
In 1993, a two-volume dissertation was completed entitled: The Petroglyphs and Pictographs of Missouri: A distributional, stylistic, contextual, temporal, and functional analysis of the state's rock graphics.
In spite of its 750 pages, it is still an overview. There is much to
be done yet.
However, it contains documentation for the 135 known sites (as
of 1993 -- we are still receiving leads to sites) with an appendix of line
drawings containing sketches of each site (some sketches being done by
avocational archaeologists before I was even born!), terminology, descriptions,
etc.
Volume I consists of intro, analysis, discussion: major motif types, motif distribution (also mapped for the 50 major motifs), cautious interpretation in view of a number of factors including the mythology of native groups from the general area.
I have assembled a team of specialists and we are currently seeking funding to date the pigments at a number of the sites.
Research continues.
The Iron Age is particularly interesting in Camunian Rock Art for the abundance and the variety of figurative themes.

In Anati's chronology (1) the Iron Age corresponds to style IV, put in sub-groups by De Marinis (2) and Fossati (3), that is:
Rock 20 of the Redondo site, in the Capo di Ponte municipality, is rich in innumerable engravings attributed to the IV style, like a lot of rocks in Valcamonica. It is a completely exposed vertical surface , 6 metres long and 4 meters wide. It is sandstone, like most of the engraved rocks in Valcamonica. The rock is placed on the orographic right side of the Oglio Valley. The area is characterised by the presence of a considerable group of engraved rocks, studied in 1970 by Paul Louis Van Berg and R.C. De Marinis.
Starting from 1993 I studied and traced this rock for my thesis.
The rock has 163 figures engraved with the hammering technique:
The 132 superimpositions among the figures permit the establishment of 4 phases:
The artefact figures are very important within the scratched engravings:
the 5 knives with sheath are comparable with the Benvenuti knife (VI-V
Cent. BC) of the near Este culture. It is very difficult to establish the
meaning of these engraved knives on the rock: perhaps they are ritual and
symbolic weapons. In fact in the Iron Age the weapon figure is not a pars
pro toto symbolising the man figure as in the Copper Age. Also the
pot figure can be placed in the sacred or ritual world: it is a one-handle
jug, with spout and conical body, like a Schnabelkanne.The pottery
figures are very rare in Camunian Rock Art.
The hammered engravings of Rock 20 are more varied compared to the scratched figures. They are of IV 3-4-5 styles, that is from naturalistic style to decadence. A pregnant mare figure is very interesting, with the little horse in the womb. The type of the engraving seems one of the X-ray engravings, present also in India and in the Sahara Rock Art. For the Valcamonica this is an unicum.
In Camunian Rock Art the figures of warriors, of duels, of weapons, of ritual pots, of hunting in the Iron Age are connected to the youth initiation rites of the aristocratic warriors. The engravings are like gifts to the Gods on occasion of these rites.
Pictures (from top):