The Lewis & Clark County Sheriff's Office is searching for an adult female horseback rider in the McMaster Hills Recreation Area several miles northeast of Helena.
Search & Rescue units from Lewis & Clark County and Jefferson County are on the ground.
Drones from several law enforcement agencies are searching by air.
A helicopter from Great Falls has also been called in to assist.
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Officials will be active in the recreation area throughout the majority of the day.
If you have information or would like to offer assistance, please call 406-219-7380.
No other details have been released at this point, including the name of the missing woman.
We will update you if we get more information.