The fog came in on 

DINOSAUR FEET filling the

      springtime afternoon.

 

Yup - this reflects a poem by Carl Sandburg from 7th or 8th grade, and remembered all these years -

The fog comes 

on little cat feet.

 

It sits looking

over harbor and city

on silent haunches

and then moves on.

 

The fog yesterday was not any "little cat feet" - it was think and dense.