During a trip to survey booming oil development in North Dakota on Tuesday and Wednesday, Interior Secretary Sally Jewell said she saw evidence energy companies are working aggressively to pare greenhouse gas emissions ahead of federal regulations on the practice.

During her two-day visit to North Dakota, Jewell visited an oil rig working for Oklahoma City-based Continental Resources, a major operator in the Bakken and Three Forks plays of Montana and North Dakota. She also toured facilities operated by Norway’s Statoil, which has invested more than $4 billion in the region.

It was Jewell’s first visit to the surging oil region since she became Interior secretary in April.

“It’s extraordinary how much oil is in the ground here and is being produced,” she said in an interview. “North Dakota has become the second-largest producer of crude oil among the 50 states. It has passed Alaska. It has passed California.”

“To see that on the ground is amazing,” Jewell added.