This "diamond" is in the "heart" of the Triangle area in a location
that highlights the difference between the past and the present.
Look one way from the cache and see how this whole area used to
be - a lovely peaceful natural forest with birds chirping and
occasional deer and other wildlife roaming about.
Turn around and see the present - a man-made concrete clearing
with a never-ending stream of vehicles zipping along (usually) at
65 mph (or maybe 70 or 80).
Please don't even think about parking on I-40 and walking to
this. In additional to being illegal and dangerous, there's a fence
between I-40 and the cache site.
Recommended parking is at N 35 53.372 W 78 50.701. From there
it's about a 200 yard slightly uphill walk along an old dirt/grass
road. Note the old fire hydrant along the way that seems rather out
of place. The cache is just a short distance off the dirt/grass
road.
The "diamond" is an emerald pill bottle just a few feet from a
large number of squares.
Before coming out to this one you might want to solve the puzzle
for my
US Geography Quiz #2 (if you haven't already) and find that one
while you're in the area.