This song is a great example of the "boogie rock" genre. Boogie rock came out of blues-rock and tends to feature a repetitive, driving rhythm, and a laid-back attitude with no sign of being pretentious. In the US, think ZZ Top and Lynyrd Skynyrd. In the UK, the vanguards of boogie rock were Status Quo, Humble Pie, Savoy Brown, and Foghat. The Doobie Brothers might get a nod here as well; Foghat started out in the UK but transplanted to the US, and the Doobie's "China Grove
" had come out only two years before. Boogie rock and mid-1970s' pot culture also went along extremely well together, which certainly didn't hurt its popularity any.