Geology and history may seem like odd bedfellows. The subjects are taught on different sides of the local community college, sternly split into two disciplines: physical science and humanities.
However, to professor Keith Meldahl, geology is history written on a much grander scale - millions and billions of years versus centuries. Taken one step further, Meldahl argues that the geology of the Southwest profoundly shaped the history of California.
Meldahl presented his findings about how terrain dictated the settlers' move west, which form the basis of his first book, "Hard Road West: History and Geology along the Gold Rush Trail," at the Solana Beach Library's Friends Night Out in March.
"Much of the route was controlled by geology," said Meldahl, who teaches at MiraCosta College. "Rivers gave them water, and mountains got in the way."
The majority of California settlers began the 2,000-mile journey at the Mississippi River in what is now Nebraska. The first half of the ride was relatively easy across the plains.
"You could go as fast as an ox could walk, about 15 miles a day," said Meldahl, who spent several months following the trail by car and foot.
The halfway mark of the settlers' five-month trek was the first pass through the Rocky Mountains and where they met up with the Humbolt River.
"Most people have never heard of it, but it's one of the most important rivers in the history of California because it flows mostly west," Meldahl said.
Most of the rivers between the Rockies and the Sierras run north to south like the mountain ranges, making water more difficult to find. The steady source of water heading in the same direction as the immigrants provided a critical lifeline for this difficult part of the journey, which Meldahl compared to going over a washboard.
Things got much more hairy the last 500 miles.
Between the two mountain ranges is a great basin, a giant bowl covering all of Nevada and half of Utah that prevents water from leaving its boundaries.
Rivers, such as the Humbolt, simply disappear or evaporate into briny pools of mud and salt (hence the Great Salt Lake). Travelers would have to stock up on this disgusting water to survive the next leg of the journey, a 40-mile stretch of desert, Meldahl said.
While not many people perished in the scorching sand dunes, hundreds of animals did, forcing some to abandon their wagons.
The final hurdle was the high passes of the Sierras. Some tried to go around them, heading north into Oregon. But that added another month to the journey, so most headed straight on, cutting through either Donner Pass to the north or Carson Pass to the south.
While chasing wagon ruts - "you can still see scars where wagons rolled through in 1849" - Meldahl took the published diaries and writings of the '49ers, reading passages where they were written more than 150 years ago.
"It was eye-opening," Meldahl said.
The bare terrain of the Southwest is a geologist's dream - no plants covering up the rocks, he said.