In Califonia cause of the ST Andreys fault line where the PACIFIC PLATE and the NORTH AMERICAN PLATE slide pass each other.
Thus, my ballpark estimated cost (basically for the AT&T conference call, $50 witness fee, $150 process server's fee; $400 deposition transcript, $25 for copying costs, and about 10 hours of legal work amount to a grand estimated total of about $625 plus 10 hours of legal work.
Another benefit of taking depositions is to preserve a witness's recollection while it is still fresh, since the trial may still be months or years away. When a witness's testimony in open court is inconsistent with that given at deposition, a party can introduce the deposition to impeach (or contradict) the witness.