Kopher means something by which one covers something, hence pitch. The
derivation of the pitch, whether it be petroleum, or botanically based,
is not relevant to its definition.

http://www.worldwideflood.com/ark/pitch/pitch.htm

Noah's ark core samples and the Heelstone core samples contain a
residue of Pinus palustris pine tar from the Longleaf pine. Pinus
palustris, after Philip Miller, botanist.

http://www.maritime.org/conf/conf-kaye-tar.htm

Any pine trees in Southeastern U.S.?