Paul Kellogg Theobald Jr.'s passion for his work at the U.S. Geological Survey spread to his family and younger American and foreign geologists alike.

"In my earlier years, I was his field assistant in part," recalled daughter Mary Doherty. "I toiled behind him and carried his samples." Today, she is a geochemist in Reno.

Daughter Catharine Eppinger of Nederland became a veterinarian instead. "I claimed to be the black sheep of the family. So I went and married (a geologist)," Eppinger quipped.

Mr. Theobald, a Stanford University graduate who spent his career at the USGS, died at his home in Golden on July 16. He was 76.

Family and former colleagues say Mr. Theobald was well-known for his work with stream sediments and mineral concentrates and for mentoring young geologists, both in this country and internationally.

Mr. Theobald worked in Saudi Arabia for two years and traveled for work to Europe and China.

He was a founding member and former president of the Association of Exploration Geochemists and was a recipient of the Meritorious and Distinguished Service awards from the Department of the Interior.

"He was my first mentor," said Lori Filipek, of Arvada. "He taught me and guided me through the learning process of being a research scientist."

That was in 1979, just after Filipek had completed her doctorate in geochemistry and oceanography at the University of Michigan.

"There weren't a lot of women doctoral scientists when I came (to the USGS)," said Filipek, now a consultant in environmental geology. "Back in the late 1970s, women weren't as well respected. He treated me like an equal scientist."

Mr. Theobald's work in the region helped lead to the discovery by the Climax company of additional ore deposits, Filipek said, which resulted in the development of the massive Henderson molybdenum mine in the late 1960s and 1970s.

Doherty recalled her father frequently taking the family on field trips in Colorado, during which they would stay in a cabin or tent camper.

"Many family conversations at dinner were about geology," Doherty said. "I think it gets into the blood."

But daughter Eppinger said there was another side to her father as well.

She said her father and her mother, Jean, who still lives in their family home in Golden, wanted their children to be aware of politics and other cultures, and those topics also spawned frequent dinner conversations.

"He had been a debater in high school and college," Eppinger said of her father. "I used to get so upset because whatever side I took, he would take the opposite one, and I always felt like I'd lose no matter what," she laughed.

Eppinger also described her father as an "incredible woodworker" who made musical instruments ranging from dulcimers to an Irish harp and was halfway through a Mozart piano when he died.

For more than a decade before the girls went off to college, the Theobald family would gather every Sunday night and play music, Eppinger said.

Mr. Theobald usually played a tenor recorder, with their mother on the keyboard, and Eppinger and Doherty on a flute and violin, respectively. "There were times when I thought, 'Do I have to do this?' but I had a really good time," recalled Eppinger.

In addition to his wife of 53 years and his two daughters, Mr. Theobald is survived by grandchildren Paul and Rosemary Eppinger; Jonathon, Jessica, Zachary and Stephany Doherty; and sister Martha Peterson, of Reno.

Mr. Theobald requested there would be no funeral service.

Contributions may be made to the charity of one's choice or the Distinguished Geochemist Scholarship Fund, P.O. Box 26099, Nepean, Ontario, Canada, K2H9R0.