I wonder how uniform Martian soil is. We have explored only a tiny fraction of the surface with actual robots. On Earth there is a huge variation between different regions. I would expect it to be similar on Mars.
Martian regolith is believed to be fairly uniform across the planet, and this is backed by analysis at several widely-scattered locations. The dust is definitely well-mixed, but coarser parts are mostly of local origin and can vary, but because of the lack of biological elements are much less varied than on Earth.