By 11:35 AM PST, the Lilac Fire had reached 500 acres (200 ha).

Fanned by unusually powerful Santa Ana winds, with gusts reaching 66 mph (106 km/h), the wildfire quickly grew in size within minutes, the wildfire grew to 50 acres. The fire was spotted near Old Highway 395 and Dulin Road, near the intersection between State Route 76 and Interstate 15, in Bonsall, San Diego County, California. The Lilac Fire was reported on December 7, 2017, at 11:15 am PST, as a small brush fire, just off Interstate 15. On December 7, the Lilac Fire also cut the power to 20,000 people. During the fire, an estimated 10,000 residents were forced to evacuate, while a total of over 100,000 residents were forced to or advised to evacuate. The fire threatened the communities of Bonsall, Oceanside, Vista, Fallbrook, and Camp Pendleton.

The fire cost at least $8.9 million (2018 USD), including $5 million in firefighting expenses and property damage, and an additional $3.9 million in cleanup and erosion control costs. The fire was first reported on December 7, 2017, burned 4,100 acres (1,659 ha), and destroyed 157 structures, before it was fully contained on December 16. The Lilac Fire was a fire that burned in northern San Diego County, California, United States, and the second-costliest one of multiple wildfires that erupted in Southern California in December 2017.

California wildfires 2017 map