Question: Telegraph Call for "End of Track"

From: pravoslavna@comcast.net

... being an old telegrapher, I'll bare that question which is burning in the back of my mind...

As the construction was pushed eastward, and the telegraph line was strung each evening into the office car so that reports could be "sent back" to the important people in Sacramento, what "office call" (combination of letters) was used to represent the telegraph office at the "end of track" ? (And, please, may no one spoof the List by suggesting that "ET" was the office call, because those two letters, along with the letter "L," were almost never used in telegraph "office calls," for reasons I won't go into here.) ...

– Abram Burnett