The Iron Horse Trail bridge over Treat Blvd is going up during the next three weekends (June 4/5, 11/12, 18/19). Treat, and likely the Iron Horse Trail/Jones Street, will be closed from 9:00 PM until 10:00 AM, so if you ride through this area on Saturday or Sunday morning you may not be able to get through. If the intersection is closed to bicycles (they have a huge crane to lift the bridge sections into place), you can take Iron Horse Trail south to the Canal Trail, then Cherry Lane back to Treat (although I don’t think that many people ride bikes along Treat anyway).
Here’s the web page with more information: http://www.ci.pleasant-hill.ca.us/CivicAlerts.aspx?AID=171