California physician Marci Bowers explains why having gender-affirmation surgery matters to some transgender people. (Whitney Shefte/The Washington Post)

Marci Bowers’s voice is throaty and whiskey-smooth. She tends to speak sotto voce and exudes a quiet confidence.

As an obstetrician, she delivered more than 2,200 babies. As a 58-year-old surgeon, she has performed 1,500 “gender affirmation” operations — and counting.

It’s the latter she understands most intimately. In 1997, Bowers underwent the procedure after a lifetime of knowing she was truly female. Three years later, she moved to the old mining town of Trinidad, Colo., to train under a pioneering doctor and establish herself as the first transgender woman to master that same surgery.

Her mentor in Trinidad was Stanley Biber, a former Army physician who’d happened into the field after a man walked into his general practice in 1969 and asked whether he could perform a sex-change operation. Biber wasn’t one to refuse a patient with a medical need, so after acquiring surgical drawings and instructions from Johns Hopkins Hospital in Baltimore — which had been doing such procedures for several years — he successfully performed his first surgery on a transgender person.

Before long, little Trinidad, population 9,000, was known as the sex-reassignment capital of the world.

Biber, then 80, told Bowers that she had “the courage, the hands and the heart” to carry on his practice — which she did, until disagreements with the local hospital triggered a move that ultimately landed her in northern California at Mills-Peninsula Medical Center.

Out of the office, Bowers teaches and lectures and, as a member of the faculty at Mount Sinai Hospital in New York City, is helping to establish the country’s first medical education program for transgender surgeons. She remains one of just a handful of physicians worldwide who does surgical reversal of the genital mutilation suffered by African women. She does so without charge.

Gender-affirmation surgeries, however, are the mainstay of Bowers’s professional life. Of the 140 to 150 she performs in a typical year, the large majority are male-to-female procedures. (The opposite remains more difficult and more expensive, with less satisfying results, Bowers said.) Her patients come from across the United States and occasionally from overseas. Seniors are no longer rare as patients.

“We’ve had over a dozen senior citizens, women in their 70s, who for one reason or another have come to the conclusion that this is the time,” she said. “A lot of people put off the surgery . . . until after retirement.”

Her waiting list is now nearly three years long.

Bill Rohr of Fort Bragg, Calif., went on Bowers’s list in the fall of 2014. The long wait tested the 68-year-old’s patience but not his resolve. At a final pre-op visit, Rohr and wife Linda sat in Bowers’s San Francisco-area office and listened as she reviewed the surgery one more time. It would be Bill’s last step to becoming Kate.

The conversation eventually segued into society’s misconceptions of transgender issues.

“Assigning gender identity on the basis of genitalia makes about as much sense as assigning it on the basis of height,” Bowers said. “Biologically, we’re much closer to each other because everyone starts out with a primordial female anatomy, so everything a male has, a female has, and vice versa. It’s just a matter of how the cards are shuffled.”

“And Marci can reshuffle them,” Rohr responded with a smile.