There are two types of placers that can be on a mountain side. When weathering attacks a gold bearing vein or bedrock deposit, and the gold is not moved and is concentrated in place by oxidation and other chemical processes, this is called an eluvial placer. When this material moved downhill by various weathering processes, it is called a colluvial placer. If this material somehow ends up in a stream or river, then it is called an alluvial placer. This is one where water is the primary mover and concentrator.