Firefighters blocked off the American River Bike Trail Friday morning after a fire quickly spread to trees and brush along the river.
"Firefighters were actually concerned about safety and crews were kept out of the area to a certain degree due to tree limbs falling," Sacramento City Fire spokesperson Roberto Padilla said.
It happened near Del Paso Boulevard and Railroad Drive, just north of the American River, around 5 a.m. Friday.
"Windy conditions helped the spread of the fire as well as very dry conditions. Obviously we are still dealing with the drought," Padilla said.
Twelve crews doused the fire with water. Five acres were left charred before it was contained.
Hot spots continued to flare, some in trees so high they had to be cut down.
"We have had a rash of fires along the bike trail. We are calling them all suspicious at this time," Battalion Chief Craig Wiedenhoeft said.
Firefighters say roughly five fires have flared in the past couple of weeks.
While they do not know who is starting them, firefighters believe they are human caused.
Nearby businesses worry and those who bike the trails are too.
"This is a wilderness area all the way up and it should not be fire and stuff. It is full of animals and stuff," cyclist John Fite said.