The two triangles that come to mind are 14, 15, 16 at Orchard Hills in WA, and 7, 8, 9 at Jawbone Creek in MT. Both have an alps hole as a commonality.
Either I don't notice them much when I play them, or triangles are not very common in my playing experience. Without searching diagrams of courses I've played the only other one I can think of off-hand is at West Cornwall, which I understand will be removed from the course in the not too distant future.