wilderness guide here
from the air, in that terrain, those towers would be visible from at least 30 miles.
It was a clear day with light winds, as shown by the direction the smoke plume took afterwards.
I base that on this;
From the top of Mt Baldy, on a clear day I can see the san fransisco peaks, 110 miles away, and a couple hundred feet lower in elevation. If one was at least 1000 feet higher than the desired target, visibility would increase.
Considering that the air in the city contains some smog, and humidity, 30 miles is a conservative estimate. It was probobly visible from a distance 2 or 3 times that, but to be conservative, 30 miles is my guess.
However; the evil midgets flagship can see a lot further than that. Based in space, they can literally see from maine to florida, from the coast to the mississippi, and in great detail.
As everyone now knows,a race of evil space midgets are responsible for the destruction on 911.