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Aspen groves on southern Utah's Boulder Mountain could be 10,000 years old, says a nature writer who is author of a new book on the trees, "Aspen."

Ann Zwinger, who has written many nature books, traveled extensively through Utah and Colorado to write this one. Zwinger and photographer Barbara Sparks, who took pictures for the book, are scheduled to speak at noon Saturday in A Woman's Place Bookstore,1400 S. Foothill Drive. Both live in Colorado Springs."The aspen in Utah are just spectacular, because you have everything from clone after clone

across the whole mountainside, to those groves with the huge aspen on Boulder Mountain," Zwinger told the Deseret News Thursday. A clone is a group of aspen trees that all grew by shoots from an original tree.

"I think we saw more red aspen in Utah than we did anywhere else, which makes them very distinctive," she said. While most aspen are bright yellow in the fall, the red subspecies is a more russet color.

Aspen growing in southern Utah could date to the Pleistocene Era, she said. "They could be 10,000 years or so old. That's just conjecture, of course, because nobody knows. "But the aspen farther north in glaciated country, in Montana, are very different from the aspen in Utah," and there is speculation that the Utah variety showed up 10,000 years ago.

To grow from seeds, aspen need a lot of moisture - a wet climate. "That would have been true in the Pleistocene (the last ice age), as it is not now," she said. "Those trees simply could have survived over the millennia by reproducing vegetatively - so that there's the suspicion that where there are a lot of aspen clones, that those trees have been there a long time."

Aspen on Boulder Mountain are spectacular for another reason: their size. Individual trees seem to be older than most aspen, beside the great age of the clones, which keep growing from the original genetic stock even though individual trees die.

"Those great big ones down on Boulder Mountain are probably 200 years old, which is way past normal lifespan. They're fairly short-lived trees, from 100 to 150 years."

Aspen are difficult to date, because they have strange tree rings. The trees are "so subject to disease, which interrupts the rings' succession."

In the LaSal Mountains near Moab, the women had "one of our big adventures," she said. "Wouldn't you know we hit it the first day of hunting season." So many hunters were driving through the region, that "we retreated off the mountain."