Most of us geezers were a little too young to have witnessed the birth,I did some,being born in '53,I remember hearing Elvis on the radio and hearing that Buddy Holly had been killed,and watching my uncle's band practice R&B at home....but that was the beginnings,I feel that when the Beatles hit the airwaves it really exploded and the British "invasion" had started.
Then it progressed by leaps and bounds fueled in part by an infusion of weed and LSD. into what most people think of '60s rock.
A thing about weed,black musicians were using it many years before the hippies were introduced to it....it was a staple in the diet of blues and jazz players.....a black guitarist turned a friend of mine onto it in 1960 in South Mississippi....way before hippies came along....and also those guys down in the Gulf coast region were well aquainted with "magic" 'shrooms.