Dying Thujas

[BWC1950]

We purchased 17 Thujas in October of 2009. They were planted immediately. We are sending you pictures of several Thujas which appear to be dying and we don't know why. They are watered regularly. We thought, at first, they were being attacked by something but unsure of what. The other idea is the Thujas, which are surrounded by rock, may be getting too hot, but we don't know and we need your help to help us diagnose the problem before it's too late. Is it rocks/heat? Is it moths of some sort? Is it the soil? Is it too much water? We live in Northern California, in the foothills and experience summer days in the 90's, and some times hotter in the low 100's. This problem didn't appear until approximately a month and a half ago, when the weather started getting warmer. Please help.

Photos attached.