La Paz County

Harquahala Mountain Observatory

Occupied from 1920-1925, this bleak outpost sits at over 5,600' on the highest peak in SW Arizona


The Harquahala Mountain Smithsonian Observatory is a historic structure in western Arizona. It is located near the summit of the 5,681’ Harquahala Mountains, the tallest peak in southwestern Arizona. The site is accessed by a 10 mile 4x4 road that climbs nearly 4,000’. The trail and summit are incredibly scenic and have numerous recreational opportunities including hiking, camping, and additional offroad trails.

The story behind the observatory and its location on top of a rural Arizona mountaintop requires a little scientific backstory. It was the late 1800s and Smithsonian scientist Dr. Samuel Pierpont Langley was studying the climate and the sun. He believed that by measuring minute changes in the atmosphere and sun’s movement, he could find the “solar constant” and use that knowledge to accurately predict weather. A man by the name of Dr. Charles G. Abbot studied under Langley and began to test the hypothesis.

The summit of Harquahala Mountain was chosen to be one of numerous test sites. This location was chosen because of its clear weather, high visibility, and its remote location. Harquahala was one of several sites around the world that would be used to collect data. The project was privately funded and the observatory was built at Harquahala by August of 1920. Access to the observatory was via a 6 mile pack trail and all supplies had to be hiked or transported to the summit via horse & mule. Applicants for the job needed to not only have a scientific background, but also be incredibly resilient and resourceful – they would be living and working in harsh conditions. 8 scientists from the Smithsonian Astrophysical Observatory called the mountaintop home between 1920 and 1925, however, typically only a field station manager and assistant were staffed at the building at any one time.

"Northern view 1922" from Smithsonian Institute

Amenities at the top were simple and functional. Two buildings were constructed. The main building (and the one still standing today) was a two-story. The top was used for sleeping, cooking, and office space. The lower level was used to hold the delicate scientific equipment. A workshop/shed stood just south of the main building, but has since collapsed. Food had to be hauled up the mountain weekly. The closest neighbor, a man by the name of William Ellison provided animals, fresh fruits and veggies, and helped maintain the trail. The primary water source was located over a mile away and 1,000 feet below the observatory. Scientists often had to carry water for themselves to the top. Cisterns were eventually constructed at the top. They helped to channel precious rainwater off the buildings and were dubbed the “Mt. Harqua Hala Water Works” by the residents.

Present day summit: The cistern and main building remain, looking north.

"Concrete cistern built Feb. 1922" from Arizona Historical Society - Tucson.

In December of 1920, tie rods were added to the structures to provide stability. Later in 1921 corrugated iron was added to protect the fragile adobe walls from the elements. Porches, cisterns, and other amenities were added in the following years by field station manager Alfred Moore and his newlywed Chella. One of the biggest upgrades was the addition of a croquet court near the present day picnic table, used for outdoor exercise.

Connecting the observatory at the top of Harquahala with the rest of the world was always complicated. Initially a system of reflecting mirrors – called a heliograph – was used to relay messages. However, this wasn’t possible during the night or when cloud cover was too thick. Radio transmitters were constructed next to allow communication between Harquahala and the nearby town of Wendon. This required tall towers at the summit. Strong winds and storms meant that keeping these towers upright was not easy.  Finally, telephone line was ran down the mountain, via the rough pack trail. This was no easy feat but allowed those stationed at the top to have reliable communication with everyone else. Although abandoned today, the summit continues to be used for communication. Microwave towers at the top are used to help direct the water flow of the Central Arizona Project far below.

Everyday life at the top involved taking scientific measurement. No telescopes were used at Harquahala. Rather very precise tools meant for observing and measuring the sun’s rays, altitude, atmospheric temperatures, and others were used. Data was recorded and calculated by hand before being sent to the Smithsonian Institute in Washington D.C. This data was compared with other recordings from observatories around the world. After a short 5 years, a combination of severe weather, difficult access, and increased haziness closed the station on top of Harquahala. The crew and supplies were moved west to Table Mountain in southern California. In 1975 the site was added to the National Register of Historic Places.

A trip up Harquahala Mountain today is certainly easier than what the Smithsonian scientists endured a hundred years ago. A high-clearance vehicle is required and 4-wheel drive is strongly recommended if you are going to make the trip. The trail is only 10 miles long but climbs nearly 4,000 feet and has an uphill grade of up to 30% at times. An old building, concrete cistern, and numerous informational signs can be found at the top in addition to some spectacular views. Easily extend your trip by exploring other 4-wheel drive roads or hiking trails in the area.



  1. Bureau of Land Management, Informational signs at summit. 

  2. "Harquahala Observatory." Arizona Pioneer & Cemetery Research Project. N.p., n.d. Web. 21 Mar 2010. <>. 

  3. Historical photos from BLM signs at summit. Original sources: "Northern View 1922" and "Snowfall Dec. 1920" from Smithsonian Institute. "Concrete cistern built Feb. 1922" from Arizona Historical Society - Tucson.