ERO provides comprehensive cultural resource management services to achieve compliance under Section 106 of the National Historic Preservation Act. Our clients trust ERO to navigate the increasingly complex Section 106 process, from initial project development to facilitating coordination and consultation with agencies and Native American tribes. ERO’s cultural resource specialists have developed programmatic approaches for multiple undertakings including completing large-scale inventories and treatment for complex multiyear projects. Our project expertise includes water development, electrical transmission, land development, conventional and alternative energy, transportation, and Section 404 permitting.

  • Cultural resource survey and identification
  • Geographic Information Systems modeling
  • Evaluative testing; historic property treatment; Native American coordination
  • Geophysical survey
  • Historic American Buildings Survey/Historic American Engineering Record to NPS and state standards

Areas of Expertise

Section 106 Compliance

ERO conducts all phases of Section 106 compliance, including: 

  • Identification (Class I data syntheses, reconnaissance survey, and Class III intensive surveys)
  • Evaluative testing of archaeological sites (Phase II) for significance
  • Historic property treatment for adverse effects (Phase III), including excavation and Historic American Building Surveys (HABS) and Historic American Engineering Records (HAER) documentation

Native American Consultation 

Federal undertakings require that agencies consult with Native American tribes to further identify and consider the effects on culturally sensitive resources. ERO has assisted federal and state agencies with this requirement by identifying tribes with historical affiliation to an undertaking's APE, conducting or facilitating consultation on their behalf, and facilitating meetings for the purpose of consultation.

Historic American Building Surveys (HABS) and Historic American Engineering Records (HAER) documentation

ERO provides Historic American Building Surveys/Historic American Engineering Records Documentation (HABS/HAER) and Historic Resource Documentation under both National Park Service and state standards. HABS/HAER documentation is typically performed as part of a treatment plan to mitigate an adverse effect on a historic property, and includes high-quality photo documentation, a narrative history compiled through primary and secondary archival research, and measured drawings. ERO has completed HABS/HAER documentation for historic bridges, engineered elements of canals and ditches, buildings, and features of designed landscapes.

Predictive GIS Modeling GIS

Using Geographic Information Systems (GIS), ERO conducts predictive modeling using environmental data layers and archaeological site data to estimate the location of both surface and buried sites. Predictive modeling is especially useful during NEPA analysis when identification surveys are premature, but a reasonable estimation of resources is an expected outcome of the analysis. In dynamic landscapes such as alluvial settings, predictive modeling has the capability to estimate the number of buried archaeological sites that might be expected during construction of buried pipelines, for example.

Geophysical/remote sensing surveys

ERO uses remote sensing techniques to identify buried cultural resources, including unmarked graves and archaeological sites. Geophysical applications (ground penetrating radar, resistivity, and magnetometer) can locate buried cultural resources that are previously unknown, or quantify the extent, number, and depth of known resources. Remote sensing serves to focus mitigation efforts over large archaeological sites by maximizing time and limiting expense.

Architectural condition assessments and stabilization

ERO specializes in architectural documentation, condition assessments, and stabilization of prehistoric standing structures. Ruins preservation is generally a four-step process that requires documenting existing conditions, completing a condition assessment that identifies threats and recommends treatments, stabilizing architecture, and developing a monitoring plan to assess conditions over time. Architectural stabilization is intended to stop or slow down the deterioration of the structural remains and retain the original architectural fabric and integrity as closely as possible. For example, ERO performed ruins preservation at the Moon House complex and in Grand Gulch in southeast Utah.

ERO permit areas and clientele

  • Permitted with all federal and state agencies in our core service area of Colorado, New Mexico, Utah, and Wyoming
  • Tribal permits include the Southern Ute Indian Tribe and the Navajo Nation
  • Forest Service Permits with Rocky Mountain, Intermountain, Northern, and Southwest Regions
  • Prequalified contractor for the Bureau of Reclamation, National Park Service, and Bureau of Indian Affairs
  • ERO routinely works with the U.S. Army Corps of Engineers, the Bureau of Land Management, and engineering companies. We hold indefinite delivery/indefinite quantity contracts with the Federal Highway Administration-Central Federal Lands, Denver Water, Colorado Springs Utilities, La Plata County, and the National Park Service.

Cultural Resources Leads

Sean Larmore – Principal
Cultural Resources Manager/Archaeologist
Sean Larmore – Principal
Cultural Resources Manager/Archaeologist

Sean has practiced cultural resource management since 1996, and has served as the cultural resource manager for ERO since 2005.  He is responsible for all facets of cultural resource compliance, developing work plans, coordinating with clients and regulatory agencies, ensuring regulatory compliance and best practices, and maintaining quality assurance and control.  Sean has a broad range of Section 106 compliance experience including municipal water development, transportation, electrical transmission, vegetation management, land development, oil and gas development, mineral development, and Section 404 Clean Water Act compliance.  He is the primary lead for conducting Native American coordination and National Environmental Policy Act impact assessments.  Sean has served as principal investigatory on more than 500 projects with cultural resource components for clients such as the Federal Highway Administration, National Park Service, Bureau of Reclamation, Forest Service, Bureau of Land Management, Army Corps of Engineers, cities, counties, special districts, and engineering firms.


Kathy Croll – Principal
Senior Archaeologist
Kathy Croll – Principal
Senior Archaeologist

Kathy is a cultural resources project manager and cultural GIS lead for ERO with more than 18 years of experience in cultural resource management. She completed her PhD at the University of New Mexico in 2010 and holds federal and state permits to conduct archaeological investigations statewide in Colorado (state lands and BLM), Utah (BLM), New Mexico (state lands), and North Dakota, as well as USDA National Forest Region 2; Santa Fe, Lincoln, and Gila national forests; and within the northwest area of New Mexico (BLM). Kathy has supervised or participated in survey, testing, and mitigation phase fieldwork in Colorado, New Mexico, Utah, North Dakota, South Dakota, Alabama, Florida, Louisiana, Illinois, Missouri, Wyoming, and Belize.  Her responsibilities include project development, project management, and supervision of all stages of archaeological data collection including file search and literature reviews (Class I), sample inventory (Class II), intensive inventories (Class III), evaluative testing, and data recovery. She specializes in GIS applications and spatial analysis and ceramic technology.  As the cultural GIS lead, she is also responsible for the analysis and presentation of all cultural GIS data.