When Rockville-bred band O.A.R. played the main stage at Merriweather Post Pavilion for the first time, back in 2002, they opened with “I Feel Home,” a fan favorite that includes the lines, “I feel home/ When I see the faces that remember my own/ I feel home/ When I’m chillin’ outside with the people I know.”

Frontman Marc Roberge can still see those faces looking back at him.

“I’m looking out and there’s a lot of people out there, but for some reason, out of all these people, I can see my mom and my dad, my science teacher from high school, my neighbor, the guy I worked for at the golf course. It was like looking out and every character from ‘The Simpsons’ is in there,” says Roberge, who often went to the outdoor amphitheater with his bandmates as a teenager to see the Allman Brothers, Phish or whoever else was in town. “It was surreal to the point of comical, like, ‘We’re all in this one place, can you really believe this is happening?’ We’ve had multiple crazy experiences there that continue to make it a place of moments.”

For many music fans who grew up (or currently live) in the Greater Baltimore and D.C. area, Merriweather continues to be a place of memorable moments. The 18,000-capacity venue, nestled in the tree-lined woods of Columbia, Md., and designed by acclaimed architect Frank Gehry, opened 50 years ago Friday with a performance by the National Symphony Orchestra. Over time, Merriweather has hosted huge names (a flyer advertising the 1973 summer lineup was so stacked — Pink Floyd! Stevie Wonder! John Denver! Miles Davis! — that it went viral in February) and has become one of the rare non-corporate, non-cookie-cutter venues renowned nationally by fans and artists alike.

This weekend, Merriweather celebrates its 50th birthday with a concert co-headlined by Jackson Browne and Willie Nelson, who both have a history at the venue. Rockville native Josh Tillman, aka Father John Misty, will open the show, and Grace Potter will host and sing some songs (Sat., 6 p.m., $55-$125).

“It’s a milestone, that place,” says singer-guitarist Jason Isbell, who headlined there last month. “Most big sheds like that aren’t a lot of fun to play, but this one sounds fantastic and it looks really cool. It keeps getting better, too.”

Merriweather is in the third year of a five-year, $55 million-dollar renovation project that has added a new box office, new concession stands and bathrooms, a rotating stage, a luxe backstage (complete with two pools) and a new standalone venue. Before next season, the pavilion’s roof will be permanently raised 20 feet to give fans on the lawn a better view of the stage.

The improvements come at a time when Merriweather’s future is bright. After years of concerns that the venue would close or be redesigned, ownership was transferred last November from the Howard Hughes Corp. to the nonprofit Downtown Columbia Arts and Culture Commission. In exchange, Hughes is developing part of what used to be the venue’s main parking lots into a new business, residential and retail core. (Merriweather attendees must now choose from a series of free parking options online before arriving.) I.M.P., the production company that owns the 9:30 Club and took over booking and operations at Merriweather in 2004, recently signed a 40-year lease to continue running the venue.

Jean Parker has been a witness to most of Merriweather’s changes. She saw her first concert ever — a Beach Boys show — at the venue in 1972, started working there part time in 1977 and took on a full-time administrative job in 1983. By 1987, she’d become general manager, a role she’s held for 30 years.

“You could not build this venue anywhere else and plop it down amongst the natural environment it sits in,” Parker says. “I think that separates Merriweather from any other venue in the country.”

Columbia resident Ian Kennedy helped launch the Save Merriweather campaign in 2003, when developers were threatening to shutter it. Now he’s executive director of the nonprofit that owns the venue and he attends nearly every show, often riding his bike from home after tucking his kids into bed.

“Merriweather is the heart of the community and I think part of that setting lends itself to this feeling that you get in there,” he says. “We have a sign that says, ‘Welcome to Merriweather Post, make yourself at home.’ That is the philosophy in a nutshell and that is not going to change.”

For O.A.R.’s Roberge, whose band has played the venue 16 times, Merriweather will always feel like home. One of his most memorable performances was at 2015’s “Dear Jerry” concert, the sold-out, multi-artist tribute to the Grateful Dead’s Jerry Garcia, where O.A.R. covered “St. Stephen,” one of the Dead’s most technically difficult songs.

“They’re gonna hate us if we screw this up,” Roberge recalls thinking. “Merriweather provided us with a pass — the fact that we’d been through the ranks and paid our dues. When we got up to play that song, at that venue, we felt like we belonged there and the crowd was so cool to us. It felt like a huge accomplishment. And I’ll always have that memory of ‘Dear Jerry.’ If we did ‘Dear Jerry’ at some other place it would have felt like just another show. Instead, we felt like we were playing in our house.”

Noteworthy Merriweather moments

July 14, 1967
Merriweather officially opens with a performance by the National Symphony Orchestra.

May 25, 1969
Led Zeppelin and The Who co-headline at Merriweather — the only time the two classic rock bands would share a bill.

The venue expands the pavilion with two loge sections (adding 1,800 seats) to book a seven-night Tom Jones run in the summer.

Worries over potential violence prompt a temporary ban of rock concerts (but not pop and folk shows) at the venue.

Aug. 27, 1977
Jackson Browne records hit single “Running on Empty” live at the venue for the album of the same name.

July 21, 1978
President Jimmy Carter becomes the first and only sitting president to perform at Merriweather when he sings “Georgia on My Mind” with Willie Nelson. He’d do it again in 1980.

Aug. 22, 1996
Radiohead opens for Alanis Morissette in what (in retrospect) was one of the odder pairings at the venue.

The orchestra pit seats are permanently ripped out to create a mosh pit for Green Day’s August stop on their “American Idiot” tour.

Jan. 6, 2009
Baltimore’s Animal Collective releases its eighth studio album, “Merriweather Post Pavilion.” The band would headline the venue in 2011 and will return with Fleet Foxes on July 29 (7:30 p.m., $41-$56).

Greensky Bluegrass to christen the Chrysalis

This season, Merriweather Post Pavilion (10475 Little Patuxent Parkway, Columbia, Md.) grew a second stage. The Chrysalis, located in the woods beyond the lawn, will officially debut as a stand-alone venue this month with a show from jammy bluegrass bands Greensky Bluegrass and Leftover Salmon (July 22, 6 p.m., $40). Part venue, part futuristic-looking neon green sculpture with a canopy built out of 7,700 aluminum tiles, the Chrysalis sits within the site’s 36-acre Symphony Woods park and has a capacity of 7,000 people. (Fans can bring blankets or lawn chairs.)

It’s already hosted some festival sets, community events and film screenings (Chrysalis was developed by nonprofit Inner Arbor Trust). But the Greensky Bluegrass show will be the first ticketed concert there, a distinction not lost on the band’s dobro player, Anders Beck. “To play somewhere totally new — not just new to us but totally new, period — is exciting,” Beck says. “Who knows, maybe one day we’ll be looking back and go, ‘Oh, man, that time when Greensky opened the Chrysalis was the coolest,’ because maybe 20 years from now everyone will have played that venue.”