to test you can do a simple extraction and use a marquis reagent to test for mesc, it gives a bright orange reaction. That first plant is a Cereus, not a Trichocereus, it is unlikely to be active like San Pedro is.
There is one plant there that
might be active:
http://www.freeimagehosting.net/4igf8plants like it are depicted in some funky andean art and they are rumored to be chemically interesting but in need of formal study
it is something like tephrocactus/maihueniopsis
globular/spherical opuntioids are worth looking into further.