If one pulls up Google maps and zooms in close they will see that, in addition to these paved roads, there are dozens upon dozens of dirt roads branching off from the main roads.
For those on this thread (not you BeanE) who think that LE should be "searching" for Kyron I ask: Where should LE start? And how many manhours do you estimate that it would take to search a single mile of road, a hundred yards back on both sides? As many locals have pointed out, this is rugged, wooded terrain with thick undergrowth, and deep ravines. Kyron's body could have been dumped anywhere. In this terrain a childs body could be a foot away from you and hidden from your view. Locating a needle in a haystack would be a piece of cake compared to locating a body in ten square miles of Oregon backcountry.
If LE receives tips that lead them to suspect that Tyrons body was dumped off a certain stretch of road I am certain they will send out search teams. However for LE to blindly deploy search teams would be, IMO, an irresponsible waste of resources and dollars. Oregon LE has a tons of experience doing wilderness searches. I, for one, trust their judgment as to when it makes sense to undertake an intensive ground search.
This Wikipedia article about Forest Park contains photos that give a good idea of how dense the vegetation is the area.
http://en.wikipedia.org/wiki/Forest_Park_(Portland,_Oregon)