In December of 2010, I visited the “Casa Grande Ruins” National Monument Archeological Site. Casa Grande Ruins National Monument is in Coolidge, Arizona; just northeast of the city of Casa Grande, which preserves a group of “Hohokam” structures dating to the Classic Period (1150-1450 AD). It was about half-way between Phoenix and Tucson, AZ.

The “Casa Grande consists of the ruins of multiple structures surrounded by a compound wall constructed by the ancient people of the Hohokam period, who farmed the Gila Valley in the early 13th century. “Archeologists have discovered evidence that the ancient Sonoran Desert people who built the Casa Grande also developed wide-scale irrigation farming and extensive trade connections which lasted over a thousand years until about 1450 A.D.

“Casa Grande” is Spanish for “big house”. The name refers to the largest structure on the site, which is what remains of a four-story structure that may have been abandoned by 1450. The structure is made of caliche, and has managed to survive the extreme weather conditions for about seven centuries. The large house consists of outer rooms surrounding an inner structure. The outer rooms are all three stories high, while the inner structure is four stories high. The structures were constructed using traditional adobe processes.

Pictured below is the best preserved side of the “Casa Grande. Why did the Hohokam build this unique structure? Was it a center of government, religion, trade, education? We may never know. But certain features of the Casa Grande give us clues about it’s use.

Picture above, notice the small Circular window in the upper left portion of the west wall. This opening aligns with the setting sun on the summer solstice (June21), the longest day of the year. The square hole in the upper right wall aligns once every 18.6 years with the setting moon at an extreme point in it’s cycle. Other windows and doorways in the upper part of the building also align with the sun or moon at significant times of the year.

Pictured below, each year around the 21st of June, the setting sun peers into the Casa Grande through a hole in the upper left of the west facing wall. This event, called the Summer Solstice, marks the longest day of the year.

Pictured below, the morning sunlight passes through a pair of holes located in the opposite walls of the uppermost from on the Casa Grande.

Pictured below, these events mark the midpoint positions of the sun as it moves along it’s north-south path.

The Vernal Equinox occurs in March, and the Autumnal Equinox arrives in September. The holes are part of a system of “alignments” incorporated into the Casa Grande that helped the ancient Hohokam track of time.

Pictured below, it appears that the Hohokam devised a calendar system based on the motions of the sun and moon, and incorporated that knowledge into their architecture. Like England’s Stonehenge, the Casa Grande may have served as an astronomical observatory and calendar.

Pictured below, this unexcavated mound was a playing field probably used in the 1100s and 1200s, before the Casa Grande was built. Ramps from either end led to the court floor, which provided space for an 12 players. A large polished green stone was found embedded in the center of the field. A playing marker?

No one knows for sure, as the Hohokam took the secrets of their games with them when they abandoned the community by the early 1400s.