Anyone got information about the transcontinental land routes? I was trying recently to learn when the first fiber optics made it coast-to-coast across the US

Anyone got information about the transcontinental land routes? I was trying recently to learn when the first fiber optics made it coast-to-coast across the US (beginning to make the Long Lines microwave relay network obsolete), and I found it really hard to dig up anything at all. I know when the technologies were developed and commercialized, but had to make some educated guesses about the progress of their deployment.