SAN FRANCISCO >> Thieves in a stolen SUV smashed through the glass doors of the Wells Fargo History Museum in downtown San Francisco before dawn Tuesday and made off with up to 10 ounces of historic gold nuggets worth roughly $10,000, police said.

But rare coin dealer Don Kagin says the robbers may have difficulty selling the nuggets unless they melt them down. Word of the heist was spreading through the rare coin community, Kagin said, and dealers will be on the lookout for nuggets and coins with historical significance that suddenly appear on the market.

The three masked thieves held a security guard at gunpoint, took 4 to 10 ounces of gold from an exhibit case and got away in a waiting sedan, police said. The guard wasn’t injured.

Robbers in Northern California have targeted precious metals in museum displays before and the tactics of the heist have marked other recent robberies in the area.

Fred Holabird, a mining geologist and an owner of a rare and unique collectibles business in Reno, Nevada, called the theft a tragedy because the nuggets could be marked with the year and place where they were mined and even the miner who unearthed them.

"This is such bad news from my viewpoint," he said.

Wells Fargo spokesman Ruben Pulido said in a statement that the company is grateful no one was injured and no damage came to the historic stagecoaches displayed at the museum, located at the site where Wells Fargo launched in 1852.

In addition to the stagecoach, used in the 1860s, the museum has a working telegraph and art and historical artifacts on display.

With the SUV still wedged in the revolving doors Tuesday morning, people walking to work stopped to look at the aftermath of the robbery and snap pictures, while police surveyed the damage. Shattered glass crunched underneath the tires of a tow truck pulling the green 1992 Chevrolet Suburban from the building.

Gold nuggets also were taken in a September 2012 robbery at the California State Mining and Mineral Museum. Five men were convicted of stealing $1.3 million in gold, quartz and other valuable metals from the museum in the western foothills of the Sierra Nevada mountains.

Some of the stolen items, including a bag of ground-up quartz, were recovered. But about $12,000 worth of gold was sold to pawn shops and dealers, police said.

It was the second heist that year of valuable metals in Northern California. In February 2012, thieves made off with large chunks of gold on display in a Siskiyou County courthouse.

Other Bay Area robbers recently have crashed vehicles into businesses to steal merchandise.

Thieves last week backed a U-Haul van through the front of a Patagonia store near San Francisco’s Fisherman’s Wharf, loaded it with high-end outdoor clothing and gear and sped off.

Last year, two suspects rammed a vehicle into an upscale designer boutique in Union Square on Nov. 26 and took handbags, police said.

Thieves in May busted through the glass at the Apple Store in a bustling shopping district in nearby Berkeley to steal electronics, leaving the car behind.

Police did not reveal the value of the stolen merchandise in any of the cases. A police spokesman also said it’s too early to tell if the incidents last year and Tuesday’s theft are linked.