Topband: Apparent Multiple Resonances on a single antenna

[Bill]

I seem to recall reading on this reflector that it is possible to find
multiple resonant points on a single antenna.  Measuring my shortened
160m vertical, I find resonances at every now and all the way up through
low VHF using an antenna analyzer.

For instance, I found almost a 1:1 match on 71.29mhz and other close
matches
as I moved down to 160m.  How is this possible and where is this coming
from?
I believe it is from the surrounding physical clutter to the vertical
that
is providing these seemingly multiple resonant points.  I also noticed
the
same thing on an 80 meter vertical I had constructed at one time.
Anyone
with an answer to this?

K2WH