It was one of the great adventures of all time — Meriwether Lewis and William Clarks' two-year exploration of the unknown world west of the Mississippi River.

It was one of the great adventures of all time — Meriwether Lewis and William Clarks' two-year exploration of the unknown world west of the Mississippi River.

When the party set out in 1803, David Dalton points out, Americans knew little about the country they would travel through.

"President Jefferson believed that the West probably still contained many of the great mammals of the Pleistocene epoch, including mammoths, giant ground sloths, and perhaps others," Dalton writes.

The amazing findings of the expedition have frequently been chronicled. Dalton — a professor of biology at Reed College — interprets them from a modern perspective to show how advances such as DNA research, understanding of proteins and the latest laboratory methods provided new information about them.

The book is written in nontechnical language and contains numerous surprises for readers, including why the explorers experienced gastric distress from some foods. Or the dangers Lewis' dog faced in the salmon-rich Northwest.

"A (raw or improperly cooked) salmon diet is a risky undertaking for a dog because of salmon-poisoning disease, which can be fatal," Dalton explains.

He can't explain the dog's survival, except to speculate the Indians warned Lewis of the need to protect him.

Still, the book is more textbook that pleasure reading. Heavily footnoted, with graphs and charts, scientific names and long explanations, it would no doubt appeal primarily to those with a science bent.

"My intention is to look at the story behind the story," Dalton writes. "There is almost always a deeper issue to probe — another rock, slightly more distant perhaps to look under."

Dalton looks at the expedition's discoveries, and what is it about those plants and animals that continues to draw the interest of scientists today.

He also explains why Lewis and Clark were about 12,000 years too late to find the great mammals Jefferson expected them to find, which for some, will be worth the read.