  Low-field magnetotransport measurements on a high mobility (mu=110,000
cm^2/Vs) two-dimensional (2D) electron system on a H-terminated Si(111) surface
reveal a sixfold valley degeneracy with a valley splitting <= 0.1 K. The
zero-field resistivity rho_{xx} displays strong temperature dependence for 0.07
< T < 25 K as predicted for a system with high degeneracy and large mass. We
present a method for using the low-field Hall coefficient to probe intervalley
momentum transfer (valley drag). The relaxation rate is consistent with Fermi
liquid theory, but a small residual drag as T->0 remains unexplained.
