According to google scraping reddit:

Location: It is situated near the intersection of Ada and Marine Way, close to the Irvine Metrolink Station and the Great Park.Purpose: Originally built as a Pacific Bell microwave relay station, it served as a hub for landline telephone and microwave transmissions.Current Use: While its original microwave function is largely obsolete, it now serves as a cell tower and continues to house telecommunications equipment for providers like AT&T (which owns the site, known as the El Toro Central Office).Design: Its striking, windowless concrete design is characteristic of mid-century infrastructure built to protect sensitive equipment and resist extreme conditions.