It was the sheer scale of Casa Grande which disconnected my brain from my eyes. Or my eyes from my brain. There are thousands of tons of clay hardpan, or caliche, mixed with water and piled up four stories high in the middle of the arid desert. It's all at Casa Grande Ruins National Monument, adjacent to Coolidge, Arizona, about 50 miles south of Phoenix Sky Harbor International Airport

Water, water everywhere, but alas, the rivers are dry now

But wait! The whole reason the Hohokam were able to build this high-rise in the desert was because they had water. And not just from one fertile stream, the Gila River, which flowed from the east, but also the Santa Cruz River, which joined the Gila from the south. Alas, the Gila River, which in colonial times carried freight, is now dry as is the Santa Cruz. River.

It was an amazing civilization which traded with Mexico; parrot feathers have been found in the ruins. The Hohokam could interpret the sun and stars to observe the solstice and more complex lunar events. One of these lunar events only occurred every 18 and a half years. Holes, circular and square in opposite walls let the light through only on these solar and lunar events.

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