BLACK HAWK, Colo. (CBS4) ??? A warning written in chalk on a state highway last week threatened Gilpin County residents with intentionally set fires.

A photo of the message appeared in a resident???s Facebook page July 25th. That resident???s post said the message ??? ???We started the fires! Be ready??? ??? was left the night before on State Highway 46 near the Gilpin County Fairgrounds.

(credit: Facebook/anonymous poster, with permission)

It references two previous fires that occurred at the fairgrounds in early July.

Together, the incidents have sent unnerved residents onto social media to express their concerns.

???Keep all your senses alert. These people need to be caught and put in jail for a long time,??? wrote one person in the Facebook post???s comments section.

The two fires at the fairgrounds came during a remarkable heat wave in Colorado. Temperatures in Denver reached 90 degrees in 20 of the first 24 days in July. Several major wildfires ignites across the state and most if not all counties enacted fire restrictions or outright fire bans during that time.

One of those wildfires, the Spring Fire, has burned almost 108,000 acres of forest and 148 buildings, including many homes. A man has been arrested for starting it; he is charged with arson.

Conditions, then, were naturally ripe for heightened anxiety in a mountain town like Black Hawk.

(credit: Facebook/anonymous poster, with permission)

The previous fairgrounds fires happened July 1st and July 5th. Both are under investigation, said Gilpin County Sheriff Bruce Hartman.

Neither, he said, is indicative of arson at this time.

The first fire ignited in a three-year-old bale of hay at 2 a.m. and re-ignited at noon the same day, according to Sheriff Hartman. It is thought to be caused by spontaneous combustion.

The second fire on July 5th in a mulch pile and, says the sheriff, investigators have yet to come to a final judgment on its cause.

The nefarious road message is more unnerving, Hartman admitted. But he asked residents to stay calm.

???God Bless the First Amendment and everything,??? he said, ???but there are a lot of factors involved. It???s all people speculating and very little data backing up what they???re saying.???

Investigators are trying to figure out who wrote the message but have little to go on aside from the chalk markings.

???We can???t compromise (an investigation) by saying a whole lot,??? Sheriff Hartman added. ???It???s not much different than a homicide case. I understand the frustration from the public. (But) I think people are over-reacting. We are taking it seriously. We???re not communicating as much as people would like, but we have some rules to follow.???

Firefighters from the Timberline Fire Protection District handled both fairgrounds fires.

Fire danger has subsided as well since the late-July monsoon season swept into Colorado.

Wildfire Resources

??? Visit CBSDenver.com???s Colorado Wildfire section.

Wildfire Photo Galleries

??? See images from the most destructive wildfires (Black Forest, Waldo Canyon, High Park and Fourmile), the deadliest (Storm King) and largest wildfire (Hayman) in Colorado history.