The pair make a triumphant return to DMV on their Can’t Let Go Tour

Opener JD McPherson called the music of Robert Plant and Alison Krauss “psychedelic.” Another apt word for the 16-song set Tuesday night (June 18th — your ace reporter’s 30th birthday) would be “transcendent.”

Krauss and Plant returned to the DC region for the first time since canceling last year. Wildfire smog had drifted into the area and made amphitheater concerts unsafe for attendees and performers.

Alone, each is an icon of their respective genres. Plant is known as the voice of the revolutionary rock group Led Zeppelin; Krauss is among the most Grammy Awarded female artists of all time for her work in bluegrass music. She crossed over to the mainstream. But together, their harmonies are otherworldly.

Plant took the lead on show openers “Rich Woman,” “Fortune Teller,” and “Can’t Let Go,” the latter of which saw some haunting vocalizations from Krauss. She sang lead for the first time on the Everly Brothers’ classic “The Price of Love.” Her twangy vibrato soared across the pavilion and into the lawn at Wolf Trap, the only National Park for the Performing Arts.

Plant, for his part, still has that famous tenor. But in the Plant-Krauss catalog, he explores the gentler, subtler side of his voice. Soft singing often morphed into a whisper-talk that caused the crowd to have to lean in and focus on the storytelling.

Of course, Plant acknowledged his origins and gave the crowd a taste of the Zeppelin days, offering a rootsy-yet-full-powered version of “Rock and Roll” with a voice full-throttle and a strong fiddle riff.

Speaking of the fiddle, Krauss, a renowned player, broke out her instrument for the first time to bow a bridge full of longing on “Please Read the Letter.” It remained close at hand for the rest of the show. Krauss’ playing elevated every song it graced. “Gallow’s Pole” was another fiddle standout.

The stage was draped in beautiful white curtains, accented with frosted white Christmas lights along the back ruffled drop. It created a living room sense of intimacy for this genre-bending night of music.

Will the three-quarters of Zeppelin that remain reunite before Plant calls it a day? Will Alison Krauss pull back into Union Station for another album or tour? These are questions that only time and artistic urges will be able to answer. (Though Mr. Plant especially may want to respectfully take the hint; his Zeppelin covers received far-and-away the biggest reactions of the night.)

However, there is something wholly fulfilling about exploring this diverse catalog of work that Plant and Krauss have created over the better part of two decades.

Their harmonies together must be experienced live to be explained. Their combined musical skill creates something that’s not quite country and not quite rock and roll. This is music born out of innate understanding by Plant and Krauss of how they complement each other. And it makes the listener eager to hear what’s next.

Robert Plant and Alison Krauss have one more show left at Wolf Trap tomorrow, June 19th, before the tour continues. Limited tickets are still available.