Whipple's
party crossed the path of today's Interstate 40 somewhere around Pinta
and entered what is now the Petrified Forest National Park north of the
highway. They more or less paralleled the highway for 15-20 miles
and crossed back to the south side of the highway near where it
crosses Lithodendron Wash. Camp 76 was probably west of Pinta
in Dead Wash before they entered the limits of today's National Park.

Here's some of
what Whipple had to say:
December
2--Camp 76...Quite a forest of petrified trees was
discovered to-day, prostrate and partly buried in deposits of
red marl. They are converted into beautiful specimens of
variegated jasper. One trunk was measured ten feet in
diameter, and more than one hundred feet in length. Some
of the stumps appear as if they had been charred by fire
before being converted to stone. The main portions of the trees
have dark brown color; the smaller branches are of a reddish
hue. Fragments are strewn over the surface for miles.