It heads southeast through Hot Lake to Union, where it overlaps OR 237 for 0.58 miles (0.93 km).

The official description of OR 203 indicates that it ends at an intersection with OR 86 near Baker City.

Current Department of Transportation charts, however, suggest that this description is outdated.

Over the decades that followed, various sections of Catherine Creek southeast of Union were channelized to avoid impinging on the roadway.

This area of Catherine Creek has recently been the focus of restoration efforts, since some sections support high populations of threatened anadromous fish.