How to add lables/etc with eia shapefiles in R?

I'm trying to create a map of US Shale basins and I'm very new to creating maps. I have downloaded the shapefiles form the eia. I have also, been able to created a basic map with the bases plotted (please see code below). I would like to add lables/etc to this map. I believe these would be in the other files downloaded outside the shp file.

library(maps)
map("state")
shapLocation<- "C:/shapfile/shalegasbasin/"
pcontorta <- readShapePoly(paste(shapLocation,"US_ShaleBasins_EIA_May2011.shp",sep=""))
plot(pcontorta, add=TRUE,  col=adjustcolor("black", alpha.f = 0.6),  border=FALSE) 

shapefile from: http://ift.tt/1yMpy16

Description of a shapefile: http://ift.tt/ThUnJF