This is exactly what I was looking at this morning. I think he possibly spoke to her while still in city limits. IMO, she didn't know he was still following her in his car or she might not have chosen to run down 385th after all.
That is exactly what the warrant says. In addition to "[Mollie's] clothing [being] found at the scene where the body was located", "Rivera admitted to making contact with a female running in Brooklyn and that he pursued her in his vehicle in an area east of Brooklyn, Poweshiek County, Iowa."
He made contact with Mollie in Brooklyn, he then pursued her in his vehicle East of Brooklyn. She must have been terrified. He attacked her and put her in the trunk of his car, but I highly doubt he stabbed her multiple times at the time of abduction. Then, per your map, he drove South past his home to the secluded cornfield. That is most likely where he removed her clothing and stabbed her at 8:28PM during a sexual assault.