Broke down, ya think

1972 Chevy C30 MH, 402BB, 4 speed manual, 42,000 original miles.
I'm out on a buy and drive adventure with my newly acquired rig. 300 miles into a 700 mile trip the clutch pedal has gone limp ( depress it and it stays on the floor) in Clovis NM. I got it going to a hotel by turning it off at stop light and starting it in gear, quite fun

It's midnight and 30 degrees outside so I didn't do any crawling around. I figured I'd ask y'all your thoughts so when I go out in the morning I will have a few ideas to check out. Is there a clutch master (slave) cylinder?
Thanks for the rescue