The song uses a variation of D-modal tuning, or DADGAD. It's a popular technique in classic Irish music. Young liked the drone of the resulting sound.
Other songs using this technique include "Ohio
," When You Dance I Can Really Love," and "Cinnamon Girl
In Young's variation, according to HyperRush
, it's CGCFAC, described as, "A combination of 'Dropped Standard' and 'Double Dropped D.' All strings are tuned down a tone/step, and then the 1st and 6th are tuned down another tone."