R will not read shapefile / file.exists returns true

It took me a bit to get this too.

# shapefile path example:
# C:/Users/User/GIS/MyShapefile.shp

# OGR command:
library(rgdal)
readOGR("C:/Users/User/GIS", "MyShapefile")

You have to leave off the ".shp" extension as well as the last forward slash on the path.