In June 2014, the precolumbian Chiefdom settlements with stone spheres of the Diquís was added to the UNESCO list of World Heritage Sites.

[citation needed] The archaeological site of Palmar Sur is located in the southern portion of Costa Rica, known as the Diquís Delta, and in the southernmost part of the Puntarenas Province.

The site is located on approximately 10 hectares of property that was previously owned by the United Fruit Company in the alluvial plain of the Térraba River.

The monumental architecture consists of two mounds which were constructed with retaining walls made of rounded river cobbles and filled with earth.

Additionally, inspired by stories of hidden gold, workmen began to drill holes into the spheres and blow them open with sticks of dynamite.

[6] The first scientific investigation of the spheres was undertaken shortly after their discovery by Doris Stone, a daughter of a United Fruit executive.

These were published in 1943 in American Antiquity, attracting the attention of Samuel Kirkland Lothrop[7] of the Peabody Museum at Harvard University.

[9] In San José he met Doris Stone, who directed the group toward the Diquís Delta region in the southwest ("Valle de Diquís" refers to the valley of the lower Río Grande de Térraba, including the Osa Canton towns of Puerto Cortés, Palmar Norte, and Sierpe[10]) and provided them with valuable dig sites and personal contacts.

[11] Before the arrival of the Compañía Bananera de Costa Rica, a branch of the United Fruit Company, and banana plantations in the 1930s, there was dense vegetation in this area.

The UFCO entered Palmar Sur in the 1930s under the name of Companía Bananera de Costa Rica in an effort to avoid antimonopoly legislature.

[12] Today there are still agricultural fields throughout the landscape which are owned by co-ops and consist of plantain, banana, and palm plantations.

Scientific research in the alluvial plain, particularly on United Fruit Company properties, began in the 1940s with the work of Doris Zemurray Stone and Samuel Lothrop.

[14] Francisco Corrales and Adrian Badilla, archaeologists with the Museo Nacional de Costa Rica, have performed continuous research in the region since 2002.

[16] Research has continued in the region by Corrales and Badilla focusing on the archaeology and the Precolumbian political structure in the Diquís Delta.

Their objectives were to study the archaeological sites containing stone spheres in the Diquís Subregion to gain an understanding of community configuration, activity areas, sequences of occupation, and the recording of monumental architecture.

[17] Research is currently ongoing at the "Farm 6" site under the direction of archaeologists at the Museo Nacional de Costa Rica.

[citation needed] The most recent hypothesis regarding the symbolic importance of the stone spheres was developed by Melissa Rudin Hernández, a Costa Rican architect investigated the cosmovision of indigenous cultures.

[21] In the cosmogony of the Bribri, which is shared by the Cabecares and other American ancestral groups, the stone spheres are "Tara's cannon balls".