More than 200 ancient mounds surfaced beneath Ecuador’s densest rainforest canopy

An archaeological survey of Ecuador’s Andean Chocó has identified more than 200 earthen mounds and over 100 terraces spread across roughly 600 hectares of rainforest north-west of Quito, a landscape that conventional ground survey had never been able to map through the region’s dense canopy. Ecuador’s Metropolitan Institute of Heritage, known by its Spanish initials IMP, carried out the fieldwork in the commune of San Francisco de Pachijal in the parish of Pacto. Specialists have attributed the remains to the Yumbo culture, a pre-Hispanic society that occupied the north-western Andes.

The scale of what LiDAR revealed caught even the survey team off guard. Before the laser scans, the same ground had registered as a modest archaeological zone of about 40 mounds and 10 terraces, a fraction of what analysis of the point-cloud data eventually turned up once the vegetation was stripped away digitally.

LiDAR Exposes a Landscape Far Larger Than Ground Survey Found

Light Detection and Ranging works by firing laser pulses through gaps in forest canopy and timing their return to build a detailed model of the ground beneath. In terrain as steep and thickly vegetated as the Andean Chocó, that technique can surface structures that foot survey teams would need years to locate, if they found them at all.

Applied to San Francisco de Pachijal, the method more than quintupled the known mound count and roughly tripled the terrace count, according to the HeritageDaily report on the Metropolitan Institute of Heritage’s findings. The surveyed area itself represents only about two percent of the Andean Chocó, a region covering more than 280,000 hectares in total, which leaves the bulk of the ecoregion still unexamined by this method.

The 600-hectare study zone works out to roughly 1,480 acres, an area large enough to contain a small town yet small enough that it had previously registered on paper as little more than a scattering of overgrown earthworks. Multiplying that gap in detection across the unsurveyed 98 percent of the ecoregion is what has researchers describing San Francisco de Pachijal as a sample rather than an outlier.

Circular and Rectangular Structures Linked by Ancient Roads

IMP consultant archaeologist Juan Jijón said the newly mapped structures show clear evidence of deliberate human modification of the landscape rather than natural formations. Circular and rectangular constructions, connected by a network of ancient roads, point to a settlement pattern that was planned rather than accidental.

That pattern, in Jijón’s reading, ties the mounds and terraces to productive, social and ceremonial activity rather than a single isolated function. Roads linking separate clusters of structures suggest a landscape designed to move people and goods between settlement nodes, not a scattering of unrelated sites that happened to survive in the same valley.

A Sunken Structure That Points to Advanced Hydraulic Engineering

Fieldwork near the San Francisco River also turned up a sunken rectangular structure that resembles architectural elements documented at the Tulipe Archaeological Complex in the nearby communities of Gualea and Nanegalito. Tulipe is already known for carved stone pools linked to water management, and the resemblance suggests the builders at Pachijal understood how to direct and hold water using constructed basins.

Researchers see that hydraulic knowledge as part of a broader technical picture rather than an isolated curiosity. A society capable of controlling water on this terrain would also have needed the terracing and road networks the LiDAR data already show, which is one reason investigators view the site as a single integrated landscape instead of a set of disconnected ruins.

Tulipe itself, now protected as an archaeological park in a neighboring parish, is one of the better-documented examples of Yumbo water engineering, with stone-lined pools carved to hold and channel water on sloped ground. Finding an echo of that same design vocabulary at San Francisco de Pachijal, roughly a mountain range away, suggests the technique was shared knowledge across Yumbo settlements rather than a one-off solution unique to a single site.

The Yumbo Traders Behind a Still Mostly Unmapped Region

The Yumbo culture flourished from roughly 800 BC to 1660 AD as skilled traders who moved goods between coastal and highland communities along intricate mountain trail networks, according to the material culture recovered alongside the mounds. Their reach across such difficult terrain is part of why researchers now suspect the Pachijal landscape connects to a much larger network of Yumbo settlement still hidden under forest elsewhere in the region.

Trading is what made the Yumbo distinctive among pre-Hispanic Andean societies: rather than staying confined to a single ecological zone, they built and maintained trails that crossed from the humid lowlands near the Pacific coast up into the colder highlands around what is now Quito, moving goods that neither zone produced on its own. A settlement pattern built around roads connecting dozens of separate mound-and-terrace clusters fits that same trading logic at a smaller, local scale.

For IMP archaeologist Dayuma Guayasamín, the project carries a purpose beyond documentation. “The aim is to protect these sites, understand how cultural landscapes were formed and strengthen Quito’s heritage,” she said. With 98 percent of the Andean Chocó not yet covered by LiDAR, the mounds at San Francisco de Pachijal may turn out to be a small sample of a far larger pre-Hispanic landscape rather than its full extent.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

More from Morning Overview