In 1932, a pilot spotted giant human and animal figures carved into California's desert; the largest stretches 171 feet from head to toe

For decades, nobody could say how old the Blythe Intaglios really were. That changed when a study in the journal Arts put real numbers on these giant desert drawings near Blythe in the Colorado Desert of southeastern California, using a technique called rock varnish dating, specifically the cation-ratio (CR) method. The study's authors estimated that three of the site's human and animal figures are probably at least 1,000 years old.

A find no one was looking for

The story of how these figures were found is almost as bizarre as the figures themselves. A pilot flying over the Colorado Desert near Blythe in 1932 saw human shapes stretched across the ground below him. They were too big to be visible from anywhere but the air. The biggest was 171 feet head to toe, more than half a football field. These are the Blythe Intaglios, also known as geoglyphs. The Bureau of Land Management, which manages the site, said there are six figures spread out over three fenced areas: three human figures, two animal figures, and one spiral design. It remains North America's best-known example of ground art.

Carving a giant with nothing but bare hands

There was no paint or dye involved. The creators of these figures scraped away the top layer of dark, sun-baked pebbles that cover much of the desert floor, a coating called desert pavement. Below is a soil with a lighter color. Careful removal of that dark layer, following deliberately planned lines, revealed the paler ground beneath it. The result is a picture that is easy to see from above but almost impossible to see when you stand beside it.

A National Park Service nomination placing the site on the National Register of Historic Places describes this process in detail. According to the document, the exposed soil in these pictures can be quite shallow, only several inches thick, although it grows deeper towards the center of some figures. It also lists Blythe as part of a much larger group: over 100 similar structures known to exist within the corridor of the Colorado River in California and Arizona. Several off-road vehicle accidents have separately scarred parts of the surrounding desert pavement over the years. That is why fences now protect what remains at Blythe.

Who they were made for

Most scholars attribute the figures to the Yuman-speaking peoples, ancestors of the present-day Mohave and Quechan tribes. The human figures are said to represent a creator being, Mastamho, with the four-legged shape representing one of two mountain lion spirits, Hatakulya, who helped during the time of creation, according to the Bureau of Land Management. Close by, sacred ceremonial dances were performed in honor of that story. That was all anyone knew for a long time. There’s no wood, charcoal, or pottery buried inside the figures that archaeologists could send off for standard radiocarbon testing. That gap made it hard to determine an actual age.

Science finally puts a number on it

Rock varnish provided the solution to the problem. It is a thin layer with a dark surface that is gradually formed on the surface of rocks in the desert environment, depending on long-term changes in rainfall. When someone removes rocks to form a figure, the newly uncovered rocks begin their own process of forming the layer all over again.

The Arts research focused on cation-ratio dating, a method first used on rocks from the Blythe figures in a 1995 study. This latest research specifically recalculated ages for the site's two human figures and one animal figure, known together as the "Blythe Giants," rather than all six geoglyphs at the broader site. The scientists found that all three of these figures are of very similar age, averaging approximately 1,000 to 1,100 years old. This date fits the previously proposed estimate ranging between 450 and 2,000 years made by the Bureau of Land Management.

The study's authors were careful to call this minimum age, not an actual birth date. This technique can estimate only the time when this stone had started regaining its coat; the exact time of clearance cannot be established. In other parts of the Colorado River, the same research group had also estimated the age of some other geoglyphs, which dated back between about 650 and almost 5,900 years. That range shows this kind of ground art was made across a very long stretch of time, not all at once.

Why these giants still matter

The Blythe Intaglios are still listed on the National Register of Historic Places and as a California Historical Landmark. Visitors can still walk up to the fenced-off figures off U.S. Highway 95 near Blythe, though the full shapes only really come together when seen from above, as they did for that startled pilot back in 1932. The site's significance lies in its staying power. People without satellites or airplanes built something to be seen only from where they themselves could never stand. Almost a century after the accidental discovery of these figures, the ground beneath them continues to offer new answers.