As I remember, sandstorms occur there fairly regularly.
One of the first selected landings sites for MER A in the Vallis Marineris, the 2500 mile long canyon on Mars. The reason this was not chosen as the final landing site was because model simulations showed possible wind gusts of 100MPH+ and the landers retro-rockets could only correct for maximum wind gusts of 60MPH.
Granted, Gusev crater is no Vallis Marineris, but certain locations on Mars are capable of Hurricane force winds, even though, like you said, the atmospheric pressure on Mars is only 1% of Earth.