Grooves in the race.
Scratch marks in the surface of the race are caused by hard particles in the lubricant.

This type of damage should be a warning flag. The hard particles may be from spalling of the bearings or from the wear of some other wheel end component. If the cause is not evident, an oil analysis may be called for.

Etched metal surface
Etched metal surfaces are usually the result of water contamination. The water allows oxidation and the metal becomes pitted and porous.

The main sources of water contamination are a failed wheel seal or leaking hubcap.

Scored rollers
Scoring around the rollers indicates contamination of the lubricant by dirt, girt or metal particles.

By tracking down the nature of the dirt, through an oil analysis, it should be simple to pinpoint the cause. External contamination will show up as grit and contaminants from the environment. Internal contaminants will most likely be from worn surfaces inside the wheel end.