 The two heads at <unk> <unk> , with the La <unk> head , are <unk> distinct from the other known examples . <unk> de la <unk> views them as a late regional survival of an older tradition while other scholars argue that they are merely the kind of regional variant to be expected in a frontier settlement . These heads are sculpted with relatively simple <unk> ; they have squat , wide proportions and distinctive facial features . The two <unk> <unk> heads are the earliest known stone monuments from the site . The discovery of one of the <unk> <unk> heads in the nineteenth century led to the first archaeological investigations of <unk> culture , carried out by Matthew <unk> in 1938 . 
