Still, the area where you marked the red arrow is a single fence area, and the bikes were found in a double fence area. The distance from the curve on the west side to the drainage pipe is more that 150 feet, so it's difficult for me to imagine that the cyclist came around a curve and had to swerve to miss a bike that was more than 150 ahead on the path ... unless, perhaps he worded it poorly.
Looking at a 3D view, it doesn't look like there's a hill at the west side of the double fenced area:
Also, we don't know for sure that the cyclist indeed saw the bikes belonging to the two girls. I would like the police to tell us if the location where the bikes were found is the same as the location where the cyclist says that he saw a bike on the path.
Do we know for sure that the bikes were found at the gate beside the drainage pipe?