[5] A decade later, the importance of the site was confirmed when a local football club began cutting away the edges of two inconspicuous mounds to lengthen their practice field, discovering an impressive buried structure.

J. Antonio Villacorta C., the Minister of Public Education in Guatemala City, requested archaeologists Alfred Kidder, Jesse Jennings and Edwin Shook to investigate.

Kidder, Jennings, and Shook's monograph, published by the Carnegie Institution of Washington – one of the most important archaeological research entities in the history of Maya scholarship – brought excited attention by scholars to the significance of the SMA.

The processualist and unilineal cultural evolutionary theoretical orientation of the Penn State project were in sharp contrast to the Carnegie work before and to the historical, cultural-historical, sometimes epigraphy- and art-historically driven paradigm of Lowland Maya research after.

In the 1990s, Marion Popenoe de Hatch and Juan Antonio Valdés conducted excavations in the southern districts of the site, and a Japanese team investigated a large mound near the modern archaeological park.

Since their work, investigations chiefly undertaken by scholars from the New World Archaeological Foundation on the southern Pacific coast of Mexico have greatly altered this view, deepening in time the incipience of complex social and cultural events in Mesoamerica.

"[9] Scattered Las Charcas remains throughout the Valley of Guatemala mark a major occupation of the area at sites such as El Naranjo;[10] at this latter site, as well as at El Portón[11] some 50 kilometers to the north and Takalik Abaj, about 130 kilometers to the west in the lower piedmont, plain uncarved upright shaft stones called stelae, mark the first appearance of a cult of time-reckoning and which became one of the bases for the institution of Maya kingship.

The architecture of Middle Preclassic structures consisted of hardened adobe bricks that served, later, as foundations for raised platforms and pyramidal temples.

Cotton was grown as well as maize; palaeobotanical research also has identified annonas, avocados, cacao, black beans, palm nuts, plums, and sapodilla (zapote blanco).

Religious practices that would later be further developed throughout Mesoamerica were elaborating during the early Middle Preclassic at Kaminaljuyu, including the erection of mounds to serve as substructures for small shrines or funerary/administrative temples, the development of a complex pantheon of deities – probably based on some primordial mythology and cosmology of which the Popol Vuh represents a fragment – and euhemerism, an incensario and stela cult, and warfare to procure captives for royal sacrifice.

Monuments included effigies of toads, bats, owls, jaguars, and serpents; particularly important was the Principal Bird Deity, a symbol of celestial power often invoked in the iconography of kingship.

[16] Many monuments were carved with Preclassic hieroglyphic texts (Kaplan 2011), underscoring the fact that, as Coe observes, "the elite of [Kaminaljuyu] were fully literate at a time when other Maya were perhaps just learning that writing existed.

"[17] In the last twenty years, archaeologists have studied sophisticated water control systems in the southern precincts of "Miraflores" Kaminaljuyu, indicating an extensive bureaucracy and concomitant social hierarchy must have been in place to supervise and maintain the hydraulics.

All that remains in the pit burial of its original fill are worn igneous rocks, quantities of coarse sherds and human skull parts that had been cut through by the digging of the tomb.

During the Early Classic period in the Maya world, art and artifacts, as well as hieroglyphics, attest to specific intrusions by and influences from Teotihuacán at great Lowland cities such as Tikal, Piedras Negras, and Copán, although the exact nature of this presence remains controversial.

Dating to Esperanza times and later in the Classic period, twelve ballcourts have been found, possibly indicating an emphasis on the resolution of conflicts through ritual game-playing rather than war, which would underscore Kaminaljuyu's role as a nexus and intermediary between powerful foreign entities and as a religious "pilgrimage" site.

Distinctively black in color, obsidian from the Chayal beds found at sites throughout the Lowlands as well as the Southern Maya Area supports this assumption, although the specifics of control, whether formally under Kaminaljuyu's hegemony or more informally representing a vital material resource whose wealth accrued to the city more or less in direct relation to proximity, remain in the realm of speculation.

In addition to Chayal obsidian, the strategic location of Kaminaljuyu as a nexus for trade between the Pacific coast and piedmont and the Maya Lowlands – salt, fish, and shells from the coast, cacao and other agricultural products from the piedmont, jaguar skins, feathers, and other commodities from the Lowland jungles – underlay Kaminaljuyu's wealth and influence throughout the Maya world.