  We observe an unusual behavior of the low-temperature magnetoresistance of
the high-mobility two-dimensional electron gas in InGaAs/InAlAs quantum wells
in weak perpendicular magnetic fields. The observed magnetoresistance is
qualitatively similar to that expected for the weak localization and
anti-localization but its quantity exceeds significantly the scale of the
quantum corrections. The calculations show that the obtained data can be
explained by the classical effects in electron motion along the open orbits in
a quasiperiodic potential relief manifested by the presence of ridges on the
quantum well surface.
