The recently proposed new process for energetic‐muon production in the atmosphere should be tested at Mt. Chacaltaya, where the atmospheric muons with longest paths in the atmosphere can be observed. For the sake of comparing the experimental results with those of usual atmospheric muons, rigorous calculations of zenith‐angle distribution of atmospheric muons have been made for the altitude of 5200 m above sea level with energy range from 100 GeV to 100 TeV, and for zenith angles from 0° to 92.3°. Calculations are based on the extension of the Chapman function to the case of a non‐isothermal atmosphere, taking into account (i) energy‐dependent nuclear‐interaction mean free path of cosmic‐ray hadrons in air, (ii) different magnitudes of photonuclear cross‐section in the energy‐loss process of muons in the atmosphere, (iii) contributions of atmospheric muons arriving below the horizontal directions, and (iv) atmospheric structure and geomagnetic deflection. Results are compared with those corresponding to sea level. Range straggling, particularly its effect on horizontally incident muons, is investigated by Monte Carlo calculation, indicating that its effects and that of (i) on the zenith‐angle‐dependence of hogh‐energy atmosphere muons are negligible.