I had refined the image a little, moving the possible location of the bikes about 20 feet to the east, and then my computer decided to turn itself off before I had saved the image. This is the photo I posted last night. Maybe Ollipop or another local can verify the details, as I'm basing everything on maps and information from the news.
This is all based on the assumption that the cyclist's tip is related to the girl's bikes. I don't believe that the girls were forced to abandon their bikes and walk to the end of the double fence area, as I think that would be too risky (too much chance that someone would come cycling along). I think they could have gone over the fence exactly where their bikes were found, which explains Elizabeth's purse on the lakeside of the fence. She was probably there and then the purse was taken from her.