[There's currently a discussion about this on Twitter by @DanKaszeta, which is the only reason I'm re-opening such an old topic.]
As was mentioned above, this monument is visible on the November 2009 and later satellite images, but not on the ones from April 2008 and earlier.
From a rough measurement using Google Earth, the vertices appear to be pointing:
to the WNW, at approximately 288º (between 280º and 295º)
to the NE, at approximately 44º
to the SSE, at approximately 191º
There are several theories so far in the discussion on Twitter. Several have mentioned a possible radar / sidescan radar / LIDAR target, while others have proposed a more traditional survey marking use.
IMO, due to the height of this monument, the former seems more likely... a simple survey marker could have been much shorter, requiring much less concrete.
Exactly 500 NM to the WNW (at 288º) of this marker, one will find runway 12/30 (among other things) at Vandenberg Air Force Base. 1500 NM in the exact opposite direction is the western-most edge of Cuba, and Jamaica 500 NM further. All lined up in a row.
In addition to current commercial spaceport users (e.g. SpaceX), Vandenberg AFB is one of three sites where the Boeing X-37B robotic space plane / Orbital Test Vehicle (OTV) lands. The first launch was scheduled for December 2008. The confirmed OTV-1 mission launched in April 2010.
HTH,
- Jim
