Mountains to Sea Trail

If you park at Peters Canyon Regional Park or Irvine Regional Park there are a few miles of dirt track. After that it's all paved. There are maybe four street crossings along Harvard in Irvine but other than that its almost all dedicated trail with no required stops. The route goes along several drainage ways and county parks. You could park at any of them for a shorter hike. Relatively flat except for the first few miles. There are occasional "Mountains to Sea" trail markers, but the trail is often not marked all that well and locally has other names. Approximately 20 miles one way.