Preserve Calavera, a coastal North County environmental group, is sponsoring a free concert, silent auction and tour of Carlsbad's historic Marron-Hayes Adobe and surroundings May 20. Dubbed "An SOS for Open Space," the 2 p.m. event marks Endangered Species Day and will feature country music by Mel Vernon, an exhibit of student art and a tour of the Buena Vista Creek valley. The Marron-Hayes Adobe is on Haymar Drive off of College Boulevard.