Hey Robotmatrix,
WWVB does a good job to most of the U.S.
A bit tougher catch here in E . MA, but I have heard the audio on VLF radios on and off plenty of times over the years.
I have two identical Radio Shack clocks that I run side by side.
At times they work better in the window ( which is NOT open to Colorado) but they usually lock up over the course of a day or three.
I actually like to leave them in the crummy location to “ gauge “ how well VLF has been doing.
NQC