Lightning is the probable cause of the 1,000-acre fire near Camp Barkeley in Taylor County, Texas A&M Forest Service spokesman Phillip Truitt said Wednesday.
Truitt said lightning likely struck in the days prior to the fire starting and smoldered until strong winds on Sunday ignited the blaze.
Firefighters are in Day 4 of battling a blaze that started about 3 p.m. Sunday.
Earlier Wednesday, Truitt said the blaze was 70 percent contained.
"(We) do have a helicopter at (the) Abilene airport for water drops as needed," Truitt told KTXS News on Wednesday morning.
Officials revised the estimated size of the Camp Barkeley fire from 1,600 acres to 1,000 acres late Tuesday.
Fire crews are aggressively attacking a massive fire near Camp Barkeley that has entered its third day.
The fire began about 3 p.m. Sunday.
"[The] plan is to hit it hard this morning," Texas A&M Forest Service spokesman Phillip Truitt said early Tuesday. "[We] had crews on the fire all night patrolling lines and mopping up edges of the fire."
More air tanker drops have been ordered and crews on going in on foot to fight the fire, authorities said Tuesday.
"One helicopter has been ordered to the Camp Barkeley Fire," Truitt said in a Twitter message about noon Tuesday. "Should be here this afternoon if no delays."
Meanwhile, the Camp Barkeley Fire Command Post has been moved to near the "Old Settler's Grounds" in Buffalo Gap, said Lt. John Cummins, spokesman for the Taylor County Sheriff's Department.
The most recent information shows the fire 60 percent contained. About 1,600 acres have been affected by the blaze.
Evacuees were given the all clear to return to their homes at about 9 p.m Monday, after being told to leave earlier that afternoon. That included people on CR 330 (Apache Junction), FM 1235 and the northwest side of Buffalo Gap.
The winds died down Monday night and humidity rose, which kept the fire from spreading as quickly. The Forest Service urges residents to have a plan in place in case winds pick up again. A Red Flag warning is in effect for Taylor County.
Truitt said Tuesday night will be much like Monday night. They will return from the hills with the heavy equipment and continue to battle hot spots with water and hand tools.