Imaging at El Morro

Flickr Photos of the El Morro Project

See our gallery of on-site photos documenting the work at El Morro. More…

El Morro National Monument in New Mexico

The US National Park Service's home page for this famous site where ancestral Puebloans, Spanish, and American travelers carved over 2,000 signatures, dates, messages, and petroglyphs. More…

Webisode: El Morro: Inscription Rock – New Mexico PBS

Watch this 4-minute YouTube video in which Jim Kendrick, archaeologist at the national park, gives a tour of the history of Inscription Rock. More…

Center of Preservation Research at University of Colorado Denver

A university research center dedicated to the study, preservation, and sustainable use of the built environment and cultural landscapes. More…

Related Publications and Links


Documenting and Interpreting Petroglyphs and Inscriptions at El Morro National Monument

El Morro National Monument

Inscription Rock at El Morro National Monument
in New Mexico

Much of humanity's history is still tantalizingly mysterious; the secrets of the past always seem to beckon to us to probe, to identify, to uncover. The fascinating inscriptions at El Morro National Monument in New Mexico have lured visitors for centuries.

In June 2015, Cultural Heritage Imaging (CHI) embarked on a project in collaboration with the US National Park Service and the Center of Preservation Research of the University of Colorado, Denver to capture important inscriptions and petroglyphs at El Morro.

El Morro traces its origins to the 1st century when the ancient Zuni Indians developed pueblos near water sources and large sandstone structures on which they carved the petroglyphs that still remain today. Spanish settlers arrived in the late 16th and early 17th centuries, often on expeditions for silver and gold. It was during this period that the Spanish began to make inscriptions on the rock, which they called El Morro, or “the Headland.”

Many Spaniards, including missionaries, military officers, and their families, signed their names and dates of arrival into the rock, as a way of marking the stop along the journey. After the United States went to war and gained territory from the newly independent Mexico, the Americans called El Morro “Inscription Rock” and inscribed it further, adding another layer of history to the site. Many of these of these Americans were military officers, and others were pioneers, passing through while heading west. The imaging project was aimed at digitally capturing the inscriptions and petroglyphs in fine detail to aid in interpretation, education, preservation, and monitoring of the site. Many of the inscriptions are at risk from erosion of the sandstone as well as rock falls and clay wash running down the cliff face after rains. Some inscriptions have already been lost, and others are faint and quite difficult to see.

Shooting the Sarah Fox inscription at El Morro

Shooting the difficult to reach Sarah Fox
inscription. Image courtesy of Center
of Preservation Research, UC Denver.

Mysteries at El Morro

While around 2000 names have been inscribed at El Morro over time, some prompt more discussion than others. Certain inscriptions at El Morro present mysteries that intrigue local communities as well as members of the general public who try to understand the stories of early settlers.

One prominent example is the inscription by Sarah “Sallie” Fox. Fox was a twelve-year old girl who passed through El Morro as her family moved west. There are several accounts of the life of Sarah Fox, including a partly fictional children’s novel, Sallie Fox: The Story of a Pioneer Girl, by Dorothy Kupcha Leland.

At El Morro, Fox’s inscription is of particular interest to visitors, especially children who can relate to the girl’s story. However, eroding sandstone has made it more difficult for people to observe her inscription and connect with Fox’s tale. While certain light angles make it easier to see the Sarah Fox inscription, it is completely obscured during much of the day due to the angle of the sun. By applying Reflectance Transformation Imaging (RTI), the CHI team was able to bring out all of the details of the inscription.

RTI study of the Sarah Fox inscription

Resulting RTI from the image capture of the Sarah Fox inscriptions. The top image is from one of the input images for the RTI, and the lower image uses a mathematical enhancement in the RTIViewer to bring out the hard-to-read letters.

Other inscriptions prompt questions about their origins. One is the story of Don Juan Oñate, referred to at El Morro as “the Last Conquistador,” and his relations with the Pueblo people. Oñate is recognized by some as a successful conquistador for his numerous expeditions and settlements in the American Southwest. Others remember Oñate for his brutality in his interactions with the Puebloans.

One question concerning Oñate at El Morro is whether he intentionally inscribed his signature over a Native American petroglyph, or whether the petroglyph was drawn later, partly over Oñate’s inscription. The petroglyph and the inscription clearly overlap on the rock wall. Which came first? Was one a sign of disrespect for the other? The conflict between Oñate and the Puebloans may have spurred the graffiti. The question is complicated by the application of graphite in some of the inscriptions. During the 1920s, the graphite was applied by a National Park Service superintendent in an effort to preserve some of the inscriptions as well as to make them more visible. This technique is not used today. The graphite was applied to both the Oñate inscription and the petroglyph, obscuring the line order. (You can learn more about this in the interactive RTI below.)

Using Photogrammetry

The CHI team used photogrammetry at El Morro to gather geometric data from the Inscription Rock. Because this technique allows relatively quick and easy 3D capture of large areas, it was used to acquire extensive data for the project. One of photogrammetry's strengths for this type of project, which includes very fine details like those in inscriptions, is that it allowed the CHI team to collect fine detail where needed and less data for the surrounding areas and cliff faces, which show the larger context. The team turned to photogrammetry to capture large-scale parts of the site. The resulting measurable 3D data can be used into the future for monitoring the site for changes from environmental wear, and it also serves as high-quality data for the historical record. The historical record is critical because of the fragility of the petroglyphs and inscriptions at the site.

In 1636, Spanish Captain-Sergeant-Major Juan de Arechuleta and two other officers inscribed this on the rock, here translated from the Spanish, which you can see in the image below:

We passed by here, the Captain-Sergeant-Major
Juan de Arechleta and the Adjutant Diego Martin
Barba and the Lieutenant Agustin de Ynojos,
year of 1636

3D data collected for photogrammetry

Top image: Collecting the 3D data by taking overlapping images. Left: Detail of a 3D model created using photogrammetry. The detail area is approximately 86cm tall and 50cm wide. The full model was created from 93 overlapping images and comprises an area approximately 5 meters wide by 4 meters tall. The details in the callout areas are from a shaded model of the panel. A: The upper part of the 1636 inscription by Arechuleta is strong and easy to read. B: The lower part of the same inscription is faded and very difficult to see. This faded area is visible in the collected geometry. C: Deeply carved Native American sheep petroglyphs below the inscription.

Using RTI

By capturing image data from the inscriptions with Reflectance Transformation Imaging (RTI), which will continue to be used in the future by interpreters, Cultural Heritage Imaging was able to shed light on these mysterious inscriptions at El Morro.

Collection image data of the Oñate inscription

Collecting RTI image data of the Oñate inscription.
Image courtesy of Center of Preservation Research,
UC Denver.

RTI’s function as a capturing technology allows for the fine surface details of the stone to be relit interactively and manipulated mathematically by the user in a viewer. This is particularly valuable for imaging faint inscriptions on stone, wood, paint and other surfaces.

The relighting and enhancement functions in the RTIViewer have proven to be invaluable in the discernment of the sandstone inscriptions. Interpreters can view the final RTI result within the viewer to adjust the lighting and shadow of the image surface. These RTI images from El Morro present the inscriptions in greater detail than can be seen in ordinary photographs, or with the naked eye. Thus RTI aids interpreters who confront the various mysteries and unanswered questions in the El Morro inscriptions.

The RTI imaging of the 1605 Oñate inscription and the related petroglyph, described above, has contributed additional evidence to help answer the question of which came first.

Decide for yourself with the images below and interactive viewer:

RTI study of disputed Oñate inscription

RTI of a portion of the 1605 inscription of Oñate with a Native American petroglyph. Left: RTI in default viewing mode. Right: Enhanced RTI using Diffuse Gain mode.



Interactive viewer: An additional detail RTI showing only the overlapping lines were captured. The horizontal line is from the petroglyph and the numbers are from the Oñate inscription. Use this interactive WebRTIViewer to zoom in and change the lighting direction to view the intersection of the petroglyph and the inscription.

RTI and Photogrammetry: Complementary Technologies

Both photogrammetry and RTI have benefits, and the techniques complement each other well. While RTI is useful for identifying fine surface details on a wide range of subjects, photogrammetry is a tool better suited for capturing and monitoring larger objects or sites in three dimensions. RTI takes more time to set up and shoot, yet RTI images can be processed in about 20 minutes, and the resulting data is easy to work with and share with others. Photogrammetry usually requires less time and equipment to set up and shoot, but more time and computer power to process. Taking full advantage of photogrammetry can produce very large and highly detailed 3D models that may be difficult for non-experts to work with unless the geometry is extensively reduced in size and complexity.

At El Morro, the CHI team used RTI mainly for the imaging of individual inscriptions, or details of inscriptions, such as the overlapping petroglyph and Oñate inscription above. RTI is still the best tool for deciphering hard-to-read or worn material and for bringing out very fine surface details, including areas that can't be discerned with the naked eye. It is practical to use RTI on areas up to about two square meters. By contrast, photogrammetric data is easy and practical to collect over much larger areas, so the team employed it to document whole panels containing multiple inscriptions and/or petroglyphs.

Employing both RTI and photogrammetry techniques gave the CHI team tremendous flexibility to collect data that captures the details of the site material and its context.

Answering Questions in the Future

The inscriptions at El Morro are not the only ones that are at risk of deterioration, erosion, or vandalism. Other engravings in stone can be found throughout the Western United States, and are subject to the same climate, development, and vandalism risks. Rock art and inscriptions also exist throughout the world; many are the historical legacies of indigenous peoples. Many inscriptions are yet to be studied by local communities, researchers, the general public, and other groups who want to preserve and interpret them. As American history is constantly being reexamined, inscriptions like those at El Morro raise important questions for people across the country. Clearer images of these inscriptions as well as measurable recorded data enable interpreters to make great strides in preserving them and answering these critical questions.

Putting the Tools in Other People’s Hands

Shooting the Sarah Fox inscription at El Morro

Equipment needed for 3D photogrammetry:
a camera with a wide angle lens,
a monopod, and calibrated scale bars.

One of CHI’s core principles is the democratization of technology: that is, to have a greater impact on protecting cultural heritage, the necessary tools must be disseminated to the people who are stewards of the material around the world. At El Morro, CHI worked with the on-site US National Park Service staff, and local Zuni people, descendants of ancient Puebloans, discussing the history of the inscriptions as well as explaining different imaging methods for the study and preservation of the site. Exposing the people who care for our cultural treasures to digital imaging is the first step in enabling them to work on other documentation and research projects. Creating clearer and more detailed images of important cultural heritage sites can also empower indigenous peoples in uncovering their histories. Certain communities may also need the capability to store information about their cultural heritage in the event of conflict or an environmental crisis. RTI and photogrammetry are methods of preserving this kind of information in a form anyone with a camera and the desire to make high-quality representations can adopt.

Thanks to Matt Hinson, 2015 summer intern at Cultural Heritage Imaging, for developing this article.