A horizontal string of 8-10 unidentified objects with a short vapor trail hovered for 5-10 min then thrusted upward rapidly,

On 3/18/18, at approx. 9:15am, my wife and I were traveling eastbound from Modesto, Ca to Oakdale Ca.  I noticed an object in the horizon hovering with a short vapor trail.  As I focused on the object I then noticed about 8 more similar objects lined up horizontally.  I could not tell what the object looked like.  As we traveled further eastward and about 5-8 min later the first object thrust upward rapidly and disappeared.  Seconds later the 2nd and 3rd objects did the same thing.  As they moved upward the vapor trail still was short but resembled an eye of a needle.  They others that were still left were further away but continued to hover for another 5-10 min and were gone.
We have looked at the photos, and the white objects appear to us to be contrails behind high-altitude aircraft, perhaps approaching an airport to the west of Modesto, perhaps SFO.  PD