Clay? Vacuum till you think you've got it all then vacuum it again. Especially on berber. Once you've removed as much of the dry particulate as possible THEN hit it with water.
I had a job like that once. Long haired dogs, landscaping outside in a clay yard, LOTS of clay in the carpet. Another job where I was vacuuming for over an hour.
If you try to steam clean with all that clay still in there and there will still be a lot of clay still in there.
2oz/gal O2 with hotsauce and a good scrub and dwell time, rinse well. O2 rinse will work nice.