Definitely 70s! It's not so much the platform (which actually came around in the 40s, if not late 30s) as the straight-down block heel. Block heels first showed up in the 60s; before then, all heels but the lowest (1" or less) were either angled or curved and tapered to smaller at the ground than at the sole. Block heels and square toes are what characterize many 60s and 70s shoes, actually; they're pretty easy to spot.