Give the folks at the Walker Art Center and The Current radio station credit for coming up with a four-act lineup for Saturday’s sold-out “Rock the Garden” show that both reinforces The Current’s indie-rock proclivities and exudes sufficient grandeur and musical muscle to play in a festival-like outdoor setting without being swallowed.

Indeed, headliners The Decemberists have been launching ambitious attempts at a prog-folk-rock magnum opus for years now, from the five-minute “Shanty for the Arethusa” in 2003 to the 18-minute, single-song EP, “The Tain,” a year later to the eight-minute operetta “Mariner’s Revenge Song” a year after that. The title track to the “The Crane Wife” (issued in 2006 and coming in “Parts 1 & 2,” naturally) likewise is meant as an epic narrative.

All that was just table-setting for this year’s “The Hazards of Love,” an old-fashioned rock opera in the vein of Genesis’ “The Lamb Lies Down on Broadway” or The Who’s “Quadrophenia.” The brainchild behind all of the hubbub, singer-songwriter Colin Meloy, likes to cite the British folk-rock music of the ’60s as inspiration. Unfortunately, there’s no Richard Thompson-size talents around this band, and a little of Meloy’s over-the-top period pieces — like “The Hazards of Love 1 (The Prettiest Whistles Won’t Wrestle the Thistles Undone)” — go a long way. Unfortunately, there’s more than a little of it being offered. Here is a video of my favorite song off the new disc, “The Wanting Comes in Waves,” from a show last month.

I’m going for the middle two acts, Calexico and Yeasayer. The core of Calexico is the duo Joey Burns and John Convertino, whose Arizona roots come forth in songs that tap into the sway and bray of mariachi, the gunslinger melodies of spaghetti Western soundtracks, and the spare, arid linear riffs of bands like Los Lobos and Dire Straits. Recently, the Calexico pair worked with jazz-soul singer Cassandra Wilson, which attests to their atmospheric musical sophistication. Check out this live track, “Victor Jara’s Hands,” a tribute to the slain Chilean musician/activist that appears on the group’s latest disc, “Carried to Dust.” And here they are at their most pop-friendly, playing “Alone Again or” in 2006.

Yeasayer, Baltimore natives who went to Brooklyn to break through, became a huge buzz band after Austin’s SXSW festival in 2007 and the release of their spectral, apocalyptic single, “2080.” Here is a live studio version of the song, which deftly demonstrates how the group can credibly claim the chimurenga musical-political style of Zimbabwe’s Thomas Mapfumo and the quirky funk of ex-Talking Head David Byrne.

Rounding out the lineup are locals Solid Gold. Here they are covering Chris Isaak’s “Wicked Game” at First Ave, and their original, “Get Over It,” at the same venue.

“Rock the Garden” at the Walker Sculpture Garden, Saturday, June 20, 3-11 p.m., tickets are $40 but the event has been sold out.