* If you're talking about a specific river, then "Snake River" is a proper noun. It needs to be capitalized because it's the name of a particular river.
* If you're talking about any river in general, then "snake river" is a common noun. It's not capitalized because it's not a specific name, but rather a general description of any river that is winding or meandering like a snake.
Here are some examples:
* Proper noun: "I went fishing on the Snake River."
* Common noun: "The snake river flowed through the valley."