Certainly Vietnam period rip stop material. I do not recognize the shoulder patch though.
Looks most likely a National Guard unit, but what state or unit is the question.
Looks similar to a hot weather BDU, with the exception of the slanted top pockets.
What is the DSA date code on the larger tag? If it is present. Looks like predomant brown ERDL. Rich A. in Pa.
1969 Shelby GT-500 King of the Road
Knowledge is power, guard it well.
Still not sure about the shirt, but the unit patch wasn't authorized by the Institute of Heraldry until 1989. Look inside the shirt or inside the lower pockets and see if there is a larger tag. As Rich A. said, it may have a date on it.