  Measurements at 100 TeV and above are an important goal for the next
generation of high energy gamma-ray astronomy experiments to solve the still
open problem of the origin of galactic cosmic rays. The most natural
experimental solution to detect very low radiation fluxes is provided by the
Extensive Air Shower (EAS) arrays. They benefit from a close to 90% duty cycle
and a very large field of view (about 2 sr), but the sensitivity is limited by
their angular resolution and their poor cosmic ray background discrimination.
Above 10 TeV the standard technique for rejecting the hadronic background
consists in looking for "muon-poor" showers.
  In this paper we discuss the capability of a large muon detector (A=2500 m2)
operated with an EAS array at very high altitude (>4000 m a.s.l.) to detect
gamma-ray fluxes around 100 TeV. Simulation-based estimates of energy ranges
and sensitivities are presented.
