platinum triangle
n.— «He knows of at least 20 20,000-plus square-foot homes under construction or about to break ground in what he called the “platinum triangle” of wealthy areas in Los Angeles County: Beverly Hills, Bel-Air and Holmby Hills.» —“Mega-mansions are L.A.‘s really big show” by Jessica Garriso Los Angeles Times June 12, 2008. (source: Double-Tongued Dictionary)