Two spheres or disks flying together over Solano County, Ca.

My friend and I were at a 4-H summer camp in the hills east of the city of Napa, California, in early August 1969.  It was mid-afternoon.  We had a broad view eastward into clear skies to very large  summer cumulus clouds rising over Solano and Yolo counties and the Sacramento Valley.  
We watched  two large grey and beige disk or spherical objects fly across the sky from southeast to northwest.  They had no markings or lights and left no contrails.  Their color seemed to shift from beige or khaki to battleship grey when they neared and flew through the clouds.  
They must've been very large, because they appeared to be about the size of my outstretched index fingernail from a distance of several miles and at an altitude about midway among the distant large cumulus clouds which they flew through.  They flew at a constant speed, in a tandem formation with the lower one slightly ahead.  They never varied their speed or direction.  
I think they must've been travelling at around the speed of a commerical jet airliner because they covered the distance from southeast of Vacaville in Solano County to near Mt. St. Helena in Lake County in around three minutes.
Witness indicates that the date of the sighting is approximate.  PD