Welcome to... "Micro-Lesson 299"
The progression applies concepts seen played by many of the most popular classic rock bands, including the Rolling Stones, Zeppelin and AC/DC.
The riff begins from the 5th position Power-chord boogie riff off of the 5th string. It connects up into the next measure with a short, "D Pentatonic," run. The boogie riff carries on in measure two with a shift to the, "C Major," chord into the end of the measure. The chord is suspended in measure three and then released with a, "G Major," chord bringing in the final measure. The use of the, "G Major," Pentatonic scale is applied at the end of the fourth measure to either wrap up the phrase or return again back to the top.
The riff is an intermediate level example that may take some extra practice in order to develop it up to the speed that it should be performed at. Take your time if the guitar-boogie technique is new to you. Otherwise, many of the seasoned players checking this riff out will find the parts used in this riff fairly manageable to perform. Use a metronome or a Drum Machine, (set to an 8th-note beat), to build-up the overall speed /tempo of this riff. Enjoy!
Micro Lesson 299: "Key of D" Classic-Rock Riff