This all depends on what season it is, and if they recently ate, etc..
When snakes are not digesting meals, they will often move to cooler areas to lower their metabolism and conserve body mass. This is quite typical for them to do.
When they eat a meal, there is no doubt that they will self-thermoregulate to the warmer area to do so, then move to the cooler areas afterwards. If they stayed in the 60's with substantially-sized meals in their bellies, it would not be digested properly, and putrify within their intestinal tract, causing them to regurge. Snakes always move around according to their immediate needs at any given time.
~Doug
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"a snake in the grass is a GOOD thing" 
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