Arizona’s Ancient Landscape

My landscape interests usually focus on contemporary, biological issues like forest dynamics and human activity. But driving through Arizona’s desert it’s hard not to be impressed by landscape features shaped over geological time scales.

The ancient trees of Petrified Forest National Monument – preserved as quartz crystal moulds of trees buried by sediments before they decomposed – are over 200 million years old.

At that time, in the Late Triassic, northeastern Arizona was located near the equator resulting in a tropical climate and vegetation. The climate and landscape couldn’t be much more different now and the sheer scale of change (both time and location) are hard to comprehend looking out over the desert sunset.

The physical size of the Grand Canyon isn’t much easier to comprehend, even when you’re stood at the very edge of the southern rim.

By the time the Colorado river had begun carving the canyon a mere 17 million years ago, the processes leading to its formation had already been at work for around 2,000 million years (the lowest sediments at the bottom of the Inner Gorge date to around that time). Sunset here is no less timeless than in the Petrified Forest.

Compared with the forest and the gorge the Barringer Crater was created in the blink of an eye. But the 300,000 ton meteor that hit earth 50,000 years ago had probably being travelling on that collision course for a much longer time.

That these awesome features remain – so huge in time and space – reminds us how fleeting our biological landscapes are.

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