Security has been tightened at San Domenico School in San Anselmo after a group of teens on mountain bikes allegedly harassed a security guard.

“One of them intentionally coughed in our colleague’s face, making mocking comments about the pandemic and contagion,” Head of School Cecily Stock said in a letter this week to the school community. “Campus closure signs were also stolen from the tops of trails.”

“This is very disheartening,” Stock said in the letter. “We need your help to both keep our community safe and abide by current orders from our public health offices.”

Marin County sheriff’s Sgt. Brenton Schneider said the school reported the incident on March 27. The school said the incident occurred at about 4:20 p.m. that day.

According to the police report, the guard said there were “approximately 15 juveniles blocking the campus entryway and then they proceeded to ride through the campus touching things,” Schneider said. The cyclists rode away on Butterfield Road.

“A deputy responded, but we were unable to locate the juveniles,” Schneider added. “We do have the extra patrol request and deputies are regularly providing extra patrol at the school and surrounding area during their shift.”

Stock said the school campus has been closed to non-essential activities and visitors since March 25, on advice from Marin County public health officials. That includes the mountain bike trails on campus grounds that are part of a larger surrounding trail network.

Reaction from the Marin County bicycling community has been dismay, given that the coronavirus crisis has shut down school campuses as well as area parks.

“It sounds like the kids that did this massively misunderstood our campus closure and made a set of decisions that they will eventually regret — clearly not understanding the serious situation that we are all in,” Emile Mulholland, a San Domenico mountain bike team coach, said in an email.

Tom Boss of the Marin County Bicycle Coalition said he and his colleagues are helping the school through social media.

“We’ve been working with the school to get the word out that the campus is closed to all,” Boss said in an email. “You can see our posts on Instagram and Facebook, and it’s also called out on our Covid-19 resource page.”

Karen Baigrie, who lives in the Sleepy Hollow neighborhood near the school, called the teens’ behavior “shameful” in a post on NextDoor.

“As a mountain biking family and as a parent of a Drake High mountain biking team member, I was very saddened to see (Stock’s) letter arrive in my mailbox,” Baigrie said.

“I know that the local middle and high school mountain bike teams do teach trail etiquette to their riders — but maybe a refresher is needed for adults and kids alike,” she added.

Baigrie said general trail etiquette is to “slow down going past hikers and stay off the trails that are closed to you.”

“We are in this together,” she added. “Let’s act like it.”

Stock said although most of the school’s students and teachers are doing distance learning from home during the shelter-in-place order, about 30 people still live on campus, including nuns, boarding students and staff. As such, the campus is considered a long-term care facility, according to guidance from Marin public health officials, she said.

“Only those who are considered essential visitors, those faculty, staff and vendors who are essential to the operations of our boarding program” are allowed on campus, Stock said. “Most teachers are not even being allowed on campus at this time.”

“While we understand that mountain biking and exercising in fresh air and open space is key to community health, the current orders from Governor Newsom and the County of Marin are extenuating circumstances that require us to prohibit guests from using trails on the San Domenico property that lead on to campus,” Stock added.

Stock advised bike riders that “you may still use the perimeter trails above campus; you may not descend onto campus. Please help spread the word and do your part to keep our students and faculty safe.”

Mulholland said neighbors and local bikers have reached out to the school in the wake of the incident.

“It has been heartening to see the outpouring of support from fellow mountain bikers since this happened,” Mulholland said. “We look forward to a time that we can all get back on the trails together.”

San Domenico’s mountain bike team competitions, like all other Marin school athletics, have been put on hold due to the pandemic, he said.

“The team won third place in NorCal race No. 1,” Mulholland added. “(That) may turn out to be their only race of the season due to the pandemic and ensuing shelter-in-place order.”