from the Foreword:
Westwater is a role-playing game emulating the classic role-playing experience of the early 1980s, utilizing Wizards of the Coast’s OGL gaming license. It is a retro clone of sorts, in that the mechanics are those very similar to a basic version of an extremely popular fantasy role-playing game. The rules herein are highly inspired by the work of Tom Moldvay, only applied to a western theme with a few house rules.
from the Introduction:
There are two ways to play Westwater. The first is a historical style. With this style, there are no demi-human races (dwarf, elf, or halfling), no magic of any sort, and no monsters. The maps and political borders will mirror those of the particular decade you are playing in your game. This style emulates the Wild West from a historical point of view.
The second style is to play with the full rules, which enables a Wild West/Fantasy hybrid gaming experience. The political borders of the United States are different than actual historical records to reflect a more wild land- scape that includes monsters and magic.