From Brad Free's column, "Different Figures Lead To Dilemma", on the subject of the track at Santa Anita changing speed:

"It was not the first time it happened this winter. The start time for the Sham was 1:32 p.m.; start time for the Strub was 3:39. It makes a difference, according to track superintendent Steve Wood. He said new maintenance methods have created a track cushion that is an inch deeper than last winter. He said the track is slower and safer, but admits 'With more depth, it's harder to keep consistent'.
Wood pinpoints the time of day when the track changes: 'Around 3:15, the moisture rises and the track becomes wet and gets dead, and people say, he changed it'.
But Wood said he changes nothing. The harrows that change the track between races remain constant.
'The depth cannot change, but THE MOISTURE DOES CHANGE (emphasis added),' Wood said. 'It changes all the time'.
While the intention of the deeper surface is safety, it creates chaos for handicappers who use the clock-- speed figures-- as a tool".