Fire crews on both sides of the border were working steep, brushy hillsides today as a 20-acre blaze that started in Tijuana pushed into the Otay Mountain area and the east side of Marron Valley. Cal Fire firefighters reported active fire behavior through the Tijuana River drainage and spent the morning concentrating on building and holding containment lines.
CAL FIRE's incident page lists the Border 6 Fire at about 20 acres and 10% contained as of Tuesday morning. CAL FIRE reports the blaze started yesterday at 1:54 PM, placing the incident in the Tijuana River area in Marron Valley. The cause, according to the agency, remains under investigation.
Local outlets report the fire first sparked in Tijuana just before 2 PM Monday, with Mexican crews battling the flames until sunset, after which the blaze crept across the drainage into U.S. territory overnight. As noted by FOX5 San Diego, U.S. firefighters were called into the Otay Mountain Wilderness at about 10 AM today as the fire moved north.
Where the blaze is burning
The fire is chewing through remote chaparral in the Otay Mountain Wilderness and along the Tijuana River drainage, terrain that makes direct attack tough and can slow efforts to deepen containment. The same stretch of backcountry has seen several cross-border fires in recent years, including the far larger Border 2 Fire in January 2025 that burned thousands of acres and triggered evacuation orders. Coverage by KPBS highlighted how quickly that earlier blaze spread in similar conditions.
What crews are doing
Cal Fire San Diego, the agency with jurisdiction, said Mexican crews were on the line as of Tuesday morning, while U.S. firefighters focused on strengthening containment. The department's incident page repeats the estimated 20-acre size, the 10% containment figure and notes again that the cause is still under investigation. Residents in South Bay and the eastern border communities are urged to monitor local emergency channels and sign up for alerts through CalAlerts.
