orientation of 4x6 posts in retaining wall
thanks for the responses. I didn't give all the details - at maximum the wall is 3 feet, but quickly tapers to 1.5 feet - the wall is at the edge of a small hill, and is actually two walls at right angles. i plan to sink the posts 4 feet into the ground, have drainage pipe, gravel, and geotex against the wall, and compact the fill in layers.
i live in california and have had two contractors bid the job. both spec'd 2x12's, and i have had a 2x12 wall on the property for 10+ years now with no apparent degradation. however your comments are worthwhile, and i will now investigate using 4x6 timbers. thanks!