Whenever the cash ran short, he would head east to the Sierra to rob a hapless stagecoach--a double life that lasted until federal agents tracked Bart back to San Francisco after locating a handkerchief bearing a tell-tale laundry stamp.
For McGrath, Black Bart signifies more than just a colorful western character. Despite his spree of holdups, never once did Bart shoot, rob or molest a stage passenger.
"He was a gentleman," McGrath said.
In fact, he adds, his research shows that rarely were innocent men, women and children involved in violent crimes back then.
For his 1984 book "Gunfighters," McGrath pored over the remaining artifacts of the mining town populations--not only visiting the sites but scouring library shelves for diaries, newspapers and letters, jail and court documents.
The book paints a living picture of towns where women were outnumbered 10 to one by men who were "adventurous, entrepreneurial, brave, young, unmarried, intemperate and armed."
"Everything about these towns should have ended up in a blood bath, but it didn't," he said. "Like Black Bart, even the highwaymen treated their victims with the utmost courtesy and respect. In these towns, the violence was limited to saloon battles.
"Those who got hurt were willing participants and many of them asked for what they got."
These were times of armed vigilantism, when newspapers applauded acts of self-defense and most everyone walked the streets armed and dangerous.
And, unlike today, they were times when women were placed on a public pedestal, McGrath said. Granted, women couldn't vote, were discouraged from learning and generally viewed as the weaker sex. But, he said, male residents of both Bodie and Aurora were even jailed for swearing in the presence of a woman.
Near the turn of the century a California newspaper asked entrepreneur Nellie Cashman if she ever felt danger going to and from the male-dominated mining camps.
"Bless your soul, no!" she replied. "I never have had a word said to me out of the way. The 'boys' would see to it that anyone who ever offered to insult me could never be able to repeat the offense."
In the developing West, most killings were honorable duels between men who knew the risks of gunplay, McGrath argues. In contrast, today's street gangs usually choose their prey at weak moments.
Many are splattered by drive-by shootings, shot in the back by bullets that also find innocent bystanders, he says, like the recent case in which a Valley woman was shot to death in front of her 9-year-old son, even after surrendering her valuables to two gunmen.
"Such a crime would have an immediate response in both these old mining towns," McGrath said, who says he does not advocate modern-day vigilantism. "There would have been an outraged citizenry that would have gotten to the bottom of the matter immediately."
McGrath attributes the rise and varying types of violence in modern society to two factors: a deterioration of the family core and an absence of a male figure in many inner-city homes.
Over the last 40 years, he says, the murder rate in Los Angeles has risen more than 1,000%--from 81 murders in 1952 to 1,092 in 1992. It's a statistic that sends him deeper into the past for answers.
McGrath disagrees with current gun legislation and with the President's new emphasis on creating new, tougher gun laws. "We already have 20,000 gun laws on the books in the United States. It doesn't make sense.
"They're all ineffectual. They affect the law-abiding citizen and not the criminals, who don't obey them in the first place. It's like outlawing crowbars as a way to fight burglary."
Instead, McGrath believes in harsher, swifter, sometimes capital punishment as a deterrent to violent crime--like hanging day back in the Old West.
And so there are days when McGrath would prefer to hop inside a time machine and travel back to those days when men died honorably and women had less to fear.
"To be back in the days when the West was won would be to participate in one of the most epic periods in the history of man," he said. "But then again, there wasn't much surfing going on back then and that wouldn't be too much fun.
"That's one of the things you learn in a study of history, that there's always going to be trade-offs."