GARDENDALE, Tex. — From the window of her tin-roofed trailer, Judy Vargas can glimpse a miraculous world. It is as close as the dust kicked up by the trucks barreling by but seems as distant as Mars.

As you walk out of her front yard — where the chewed-off leg of an animal, probably a feral hog caught by a prowling bobcat, rots outside — a towering natural gas flare peeks over the southerly view. Across the railroad tracks and Interstate 35, a newly reopened railroad interchange stores acres of pipe and receives shipments of sand from Wisconsin to be used in hydraulic fracturing, or fracking. Next to the terminal is an expanding natural gas processing plant that lies in the heart of the Eagle Ford, a giant shale oil field that here in La Salle County alone produces more than $15 million worth of oil a day, or about one out of every 55 barrels produced in the United States.