I think this is a really neat picture! Note the two conductors on the towers at the left. This must be DC transmission. The report mentions DC transmission at 500 KV, which eases the problem of keeping widely separated generation in phase.

This is the cover picture of the report by the Federal Energy Regulatory Commission and the North American Electric Reliability Corporation, concerning the September 8, 2011 power outage.

Dustin Logan adds: The HVDC line shown in the picture is actually rated at "1000kv" (+ and - 500kv, on the two lines). Such DC lines can actually be run as two separate circuits, with earth ground acting as the return path! The line runs from a generating station in Utah, to a converter station, near Victorville, CA---roughly following the route of I-15. Here is a web page, that describes that line:

http://en.wikipedia.org/wiki/Path_27

Looking at the shot, it appears to have been taken just off of I-15, only a couple miles north of Barstow, CA (for anyone wishing to try to duplicate it). I passed by there many times, back when I lived in CA. But, unfortunately, I never got the chance to stop for a shot. I only have a couple videos of the same scene, made from a moving car, blazing south on the Interstate. The RR tracks in the foreground are Union Pacific. However, this shot is a little dated, as the UP tracks still have signal lines. From what I recall, UP removed all those lines, back in the mid 90's. There is also another good view of the lines, just off of I-40, in that same area, a few miles east of Barstow, near Daggett.

The FERC/NAERC report is here:

http://www.ferc.gov/legal/staff-reports/04-27-2012-ferc-nerc-report.pdf

See page 1 of the report for the following summary.

On the afternoon of September 8, 2011, an 11-minute system disturbance occurred in the Pacific Southwest, leading to cascading outages and leaving approximately 2.7 million customers without power. The outages affected parts of Arizona, Southern California, and Baja California, Mexico. All of the San Diego area lost power, with nearly one-and-a-half million customers losing power, some for up to 12 hours. The disturbance occurred near rush hour, on a business day, snarling traffic for hours. Schools and businesses closed, some flights and public transportation were disrupted, water and sewage pumping stations lost power, and beaches were closed due to sewage spills. Millions went without air conditioning on a hot day.

The loss of a single 500 kilovolt (kV) transmission line initiated the event, but was not the sole cause of the widespread outages. The system is designed, and should be operated, to withstand the loss of a single line, even one as large as 500 kV. The affected line—Arizona Public Service's (APS) Hassayampa-N. Gila 500 kV line (H-NG)—is a segment of the Southwest Power Link (SWPL), a major transmission corridor that transports power in an east-west direction, from generators in Arizona, through the service territory of Imperial Irrigation District (IID), into the San Diego area. It had tripped on multiple occasions, as recently as July 7, 2011, without causing cascading outages.

See page 27 for the following explanation of the root cause.

APS manages H-NG, a segment of the SWPL. At 13:57:46, the series capacitors at APS's North Gila substation were automatically bypassed due to phase imbalance protection. APS sent a substation technician to perform switching to isolate the capacitor bank. The technician was experienced in switching capacitor banks, having performed switching approximately a dozen times. APS also had a written switching order for the specific H-NG series capacitor bank at North Gila. After the APS system operator and the technician verified that they were working from the same switching order, the operator read steps 6 through 16 of the switching order to the technician. The technician repeated each step after the operator read it, and the operator verified the technician had correctly understood the step. The technician then put a hash mark beside each of steps 6 through 16 to indicate that he was to perform those steps. The technician did not begin to perform any of steps 6 through 16 until after all steps had been verified with the system operator.

The technician successfully performed step 6, verifying that the capacitor breaker was closed, placing it in "local" and tagging it out with "do not operate" tags. However, because he was preoccupied with obtaining assistance from a maintenance crew to hang grounds for a later step, he accidentally wrote the time that he had completed step 6 on the line for step 8. For several minutes, he had multiple conversations about obtaining assistance to hang the grounds. He then looked back at the switching order to see what step should be performed next. His mistake in writing the time for step 6 on the line for step 8 caused him to pick up with step 9, rather than step 7. Thus, he skipped two steps, one of them the crucial step (step 8) of closing a line switch to place H-NG in parallel with the series capacitor bank. This step would bypass the capacitor bank, resulting in almost zero voltage across the bank and virtually zero current through the bank. Because he skipped step 8, when he began to crank open the hand-operated disconnect switch to isolate the capacitor bank, it began arcing under load. He could not manage to toggle the gearing on the switch to enable its closure, so he stayed under the arcing 500 kV line, determined to crank open the switch far enough to break the arc, thereby preventing additional damage to the equipment.

At 15:27:39, the arc that had developed on each phase of the disconnect switch lengthened as the switch continued to open, to the point where two phases came into contact. This caused H-NG to trip to clear this phase-to-phase (A to C) fault. The high-speed protection system correctly detected the fault and tripped the line in 2.6 cycles (43 milliseconds). After discussion with the technician, APS operators erroneously believed that they could return the line to service in approximately minutes, even though they had no situational awareness of a large phase angle difference caused by the outage. More time would have been needed to redispatch generation to reduce the phase angle difference to the allowed value. APS system operators informed CAISO, Salt River Project (SRP), and WECC RC that the line would be reclosed quickly, even though they were unaware that this was not possible because of the large phase angle difference that existed between Hassayampa and North Gila. The inquiry's simulation indicates that the post-contingency angular difference was beyond the allowed North Gila synch-check relay reclosing angle setting of 60 degrees, and there would not have been adequate generation for redispatch to reduce the phase angle difference to within the allowed value. APS operators were only able to see the angular difference on EMS displays after isolating the North Gila capacitor bank and re-energizing H-NG from the Hassayampa substation (before closing at North Gila).