We drove to Estes Park and Rocky Mountain National Park at the beginning of April from the lowlands at the base of the Rocky Mountains. If you don’t know the area, Estes Park is the city at the east entrance to Rocky Mountain National Park (RMNP). Unless you camp in RMNP, if you come from the east, you are likely to stay in Estes Park to explore Rocky Mountain National Park.
Estes Park is a small city, not a forest reserve. There are a number of towns with park in their name at about 8000 feet on the front range of Colorado. It means a level area up in the mountains. (From the Oxford English Dictionary: "park. In some parts of the United States, especially Colorado and Wyoming: a high plateau-like valley among the mountains." )