This evening, I had a chat with one of the crew members involved in this fiasco. Some time after leaving San Luis Obispo, the second unit suffered a failure that rendered it unusable. Then, up by Castroville, the lead unit fried its computer, resulting in an emergency stop and locked brakes on the locomotive. Since this was an extraboard crew, they had not been assigned a company cell phone; they had to contact the UP dispatcher to get permission to use a personal phone, then got involved in a lengthy conference call with various "experts" back East. Once the experts were finally convinced that the lead unit's brain was fried beyond redemption, it was decided to have the UP local tow the train to Watsonville Jct., as the two rear Amtrak units (although working fine) were facing backwards so couldn't lead. Before they could move the train it had to be inspected (because of the emergency stop)--26 cars worth and no ETD on the rear. The brain-dead lead unit had to have its brakes cut out in order for its wheels to turn. The original Amtrak crew died on the law at WJ; a relief crew came and turned the power on the wye and ran the train to Oakland (where they died, having been on standy by since midnight).
Oakland Mechanical couldn't repair the two BO units, so the train proceeded with just two of the four working. I see from a more recent thread that the train acquired three BNSF units by the time it got to Seattle, but I wonder how it did getting over the Cascades on the UP. Despite the "troll alert" suggested above, this consist was indeed headed to Washington for PTC testing, or so the crews were told.