Archaeological Report

 July 12th, 2014 |    mangotree

During the V Festival of the Spheres in Palmar Norte of Osa, the civil servants of the Department of Museum Protection were in charge of a stand of the National Museum. They had a sign-in form for people interested in receiving further information of the museum. Ms. Rosemary MacGregor, owner of the hotel, “The Mango Tree Spa” in Tres Ríos de Coronado of County Osa, left a note next to her name about an archeological find (a stone with “many drawings”) near her hotel.

The information was transferred to the head of the Department of Anthropology and History, Lic. Myrna Rojas, who asked me to do a respective inspection. The inspection was made the 5th of June of 2010 with the aim of determining if the stone was worthy of preservation and attention from the Department. The field observations form the base of the present report

The property of interest where the inspection was made is in the province of Puntarenas, Osa cantón, district Bahía Ballena. Geographically, the land in question is located in the coordinates Lambert 507 600 and 334 400north, Coronado 3443 II, scale 1:50.000, published by the National Geographic Institute of Costa Rica. The Coronado River runs about 100 m. from the site. The zone comprises the lower spurs of the Costeña mountain range. The direction and way to get to this property is as follows: Crossing the Costanera highway to toward the Costeña Mts., procede 2.8 km to Tres Rios with the Coronado River on your right.

The land is the property of a foreigner whose name, direction and telephone it was not possible to obtain, since, apparently he lives abroad. The property is currently in the caretaking of Mr. William Avila, tel. 2786 54-16. The property consists of two areas flattened for houses next to the access road to Tres Ríos. The land has been used for pasture. The stone is located at an altitude of 60m. The whole surrounding area is of broken topography.

tres rios corona costa rica map

The inspection of the place was made in the company of Ms. MacGregor. The property is at the side of the road and a survey was made of the area where the stone that contains the petroglyph is located. Also, the zone where the stone was located originally was inspected. According to the compiled reports the stone was first located on the upper plantel (flattened building site) and when the land was leveled, the stone was moved close to the edge above the lower plantel. That happened around a year ago. Two men dug under the stone and then pushed it over the edge and it came to rest in the middle of the lower plantel. Apparently their intention was to remove the stone from this location. Ms. MacGregor related that she intervened to stop the removal of the stone. The previous owner of the property was Mr. Lidier Fernandez, who now resides in Ojo de Agua de Osa.

The rock remained inverted with the petrogliphs now in the inferior part. It was not possible to actually observe them but a tactile exploration was done feeling the carvings. Based in the pictures provided by Ms. MacGregor of the stone while still on the upper plantel, the petrogliphs consist of interconnected spirals, scrolls, lines and points and a distinct head of a bull. The petrogliphs cover almost all the superior face of the stone.

arqueology stones in costa rica

The stone is rounded and measures 1, 70 xs 1.75 m. with a thickness of 1,10 m. It presents exfoliations by natural causes and marks done with some hard object, perhaps metal. Ceramic materials are reported to have been found nearby but they were not observed in the inspection since the land was leveled and the bordering zones presented much vegetation.


more stones

A visit to the school of Tres Rios was made to locate another petroglyph reported by Ms. MacGregor consisting of a stone with a design of two spirals. Near the school there is an accumulation of stones that resides about 100m. from the Coronado river. The zone of stones is covered by vegetation but in a cleaned out area a stone with a petroglyph was observed representing a singlr spiral. It is possible that there were other motifs that were not clear. This stone was different from the one reported by Ms. MacGregor which could not be located due to a thick vegetative cover, but it must be verified. The stone with the one spiral measures 1,30 x 0,55 m with 50 cms. of thickness.

The location is registered as Tres Ríos (P-877- TR) and at the moment includes the two petroglyphs that need to be further inspected in the hope of finding other associated findings.

stone and arrow


The inspected petroglyph was removed from its original location by means of violent methods that affected the stone (observed marks, rolling). In it’s present position the designs are not exposed to the action of sun and rain, but they could be in danger by their continuous contact with humidity. Also, It’s proximity to the street and the lack of protection and monitoring sets it out as a target for further vandalism or removal.

The petroglyphs in the two observed stones are typical of the South zone of Costa Rica and are made up of the abstract designs of different complexity found in this area. The moved petroglyph shows the dominant motifs. The spirals are of different variations and has been associated with water (Zilberg 1982, Sol 2003).

In the near zone of the Grisera Range petroglyphs have been reported (Sol 200:132) with very similar designs comprised of the same elements. In the zone of Dominicalito, a petroglyph is reported that displays stone drawings that correspond to spirals and several lines that finish in points (Corrales 2002). (Zilberg 1982) reports diverse categories found within a number of elements and the overeall similarity to those found in the south-east of Costa Rica. The moved petroglyph would correspond to the C1 category of petroglyphs that contain diverse abstract elements connected by curvilinear lines. The petroglyph in the school on the other hand is associated to A1 category or simple elements where the spiral predominates (Zilberg 1982:345). The presence of these petroglyphs plus the reports of other evidences in the zone establishes that pre-Columbian occupations of relevance occurred and further research must be made to establish this pre-Columbian occupation and the association of these petroglyphs with other archaeological contexts.

The following actions and recommendations are given:

File a denounce at the Fiscalía de Osa of the illegal removal and damages caused to the petroglyph. In addition this vandalism was not reported by the owner of the land, making it necessary to investigate who is ultimately responsibile in this case.

To move the stone with petroglyphs to a safe place since in the present state is in danger of deterioration and theft. This must be coordinated with the entity in charge of the National Museum of Costa Rica (Department of Protection of the Cultural Patrimony) and to make the respective loan agreement. The school property of Tres Rios is recommended, since, already two other petroglyphs exist. These also need to be protected and located in a site that would preserve their value as an educational project.

To notify the Municipality of Osa of the presence of patrimonial evidence in the zone so that it is considered in the approval of future projects in the area and the proper respective studies of impact are made.

To notify the owner of the moved petroglyph that he must communicate to the National Museum of Costa Rica any act of looting from his property, or, as required, to make contact with that institution if some construction is planned, change or diversification in the present use of the land, or sale of the building.

To demand an archaeological evaluation of the zone to establish the basic characteristics of the occupation and association of the petroglyphs.