For almost 20 years, a young woman was believed to be missing in the dense Colorado mountains.

But 12 small pine needles in a clump of hair suggested that investigators narrowed their search to an area 9,000 feet above sea level.

This is how forensic plant ecology helps solve a very cold case. After graduating from college,

25-year-old Michelle Wallace decided to pursue her love of photography.

She was known primarily for her photos of people.

But she decided to try her hand at landscape photography,

and she headed to the mountainous wilderness of western Colorado.

She rode polo ponies and branded cows and went rock climbing,

and was a student at the Rochester Institute and was quite a student of photography. She was a realist and she

knew how to face things and worked through them. Michelle faithfully called her parents almost every day

to let them know where she was and what she was doing. But when several days passed without a call, her parents became alarmed.

I knew that she didn't run off.

You know, they said, well, this is one of these girls that, you know, just decides she's a free spirit.

And off she goes.

She was not that way.

When local officials were told she was missing,

they instituted what was to become the largest manhunt in Colorado history.

There were hundreds of people in the woods,

literally walking hand in hand across fields and mountains.

Search teams covered more than 3,000 square miles of isolated mountain landscape,

but found no sign of Michelle or her red station wagon.

It was as if Michelle had simply disappeared.

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