Just there 2 weeks ago... I have tmobile and it was fine in campground and lake area. But from hwy50 to campground to was spotty.
We had good cell service! We have metro. We were just there last week.
Recreation.gov has 5 reviews saying AT&T has good coverage. Verizon and T Mobile also have good coverage..
I didn't check at&t service but the campground is directly below one of the tallest peaks in the area that has multiple cell towers and a US forestry service fire station. You should be good. Other areas nearby will be spotty or no service as you come in off 50 on Ice House and depending on where you go exploring.
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