Casa Grande Ruins National Monument Historic Structures Report

The Historic Structure Report will synthesize past research to document the ruin’s history, current condition, and deterioration, outline appropriate preservation and documentation techniques, and present a comprehensive treatment history, an analysis of structural, seismic, weathering, and pest-related issues, and updated condition assessments with recommendations to support informed management decisions.

Project Overview

The Historic Structure Report (HSR) will synthesize past research to document the history, current condition and deterioration of the ruin as well as appropriate preservation and documentation techniques to provide park managers with easy access to data for informed management decisions. The HSR will include three parts. First, a comprehensive synthesis of the research and treatment history of the ruin; second, analysis of resource-specific issues related to damage caused by structural instability, seismic movement, weathering and pests (rodents, birds). Third, updated condition assessments and recommendations for future treatment and documentation of the structure.

Project Description

The Great House at Casa Grande Ruins National Monument is a 4-story earthen structure built in 1350 C.E. and is one of the largest earthen structures ever built in North America. This structure is the most dominant feature of a greater cultural landscape of irrigation canals, platform mounds, ballcourts, and domestic dwellings designed by the Ancestral Sonoran Desert people and set in the Gila River Valley near present-day Coolidge AZ. The Great House is the last remaining building of its kind in central and southern Arizona and is the reason for the National Monument’s establishment. Although it is protected by the constructed shelter, the Great House is actively deteriorating, as evidenced by significant material loss and erosion.

For instance, during high intensity rain events, moisture is drawn under the modern shelter and blown toward prehistoric walls in a "vortex effect". This moisture batters fragile wall tops, causing erosion and damage. The process causing the "vortex" is poorly understood, but may be mitigated with additional modeling and research. In addition, the structure is threatened by active integrated pest management (IPM) issues, including roosting birds and burrowing animals. Research is necessary to document the way in which animals access the structure and potential methods for excluding them and preventing damage. The nearly 700 year old structure also shows signs of structural cracking and may be susceptible to seismic activity. Materials testing, seismic vulnerability testing and structural stability assessments would be conducted to determine the susceptibility of standing walls to material failures and movement.

For over 45 years, Casa Grande Ruins National Monument has commissioned studies regarding the protection and preservation of the site. Most often, these studies focus on the structural stability of the ruin as well as deterioration and material loss caused by weathering and animals. The number of studies covering these topics is extensive and difficult for park staff to access and use effectively. As a result, the park has requested the creation of a historic structure report (HSR) which will synthesize existing information, collect and analyze new data and provide guidelines for future preservation treatment and documentation. The document will consist of three parts including 1) a comprehensive treatment history; 2) an analysis of specific issues related to weathering, structural stability and pest damage, and 3) an updated condition assessment with recommendations for future treatment and post-treatment documentation standards.

The project began in 2024 and will conclude in 2027.

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