Progression
The I–bVII–IV–I in C major
I–bVII–IV–I in C major plays C, Bb and F — I, bVII and IV — across 4 chords. The mixolydian rock cadence — a flattened seventh in place of the leading tone — behind riffs from classic rock to jam-band vamps.
The chords, in order
1CI
2BbbVII
3FIV
4CI