This is N9-56. To the right side of the structure is the mask. There is an identical mask on the left but it has been left covered to preserve it.
N9-56 stands 20m high and consists of a series of five major successive building phases; the primary structure was built in the Pre Classic about 200 BC, the latest modifications made in the Late Classic around AD 800.
From the Watercolor painting it can bee seen that there are additional masks to the one that is visible in the pictures. The additional masks are on both sides of the center stairs. These masks were unearthed but covered again to preserve them.
Photos are from 1999 and 2001.
Photos in 2001 show consolidation, repair work, being done by Louise Belanger, Home Page.