White light with diffuse blue trail seen from Los Angeles

At approximately 6:00 pm I was feeding my dogs in my northeast Los Angeles backyard.   The sky was already dark as sunset in Los Angeles was at 4:55pm.  I happened to look to the west when I saw a bright white light.
The object was approximately 50 degrees above the southwest horizon.   Emanating from the point of white light was an area of illumination resembling a cone, with the tip of the cone at the light and the bottom part of the cone shining to the east toward me.  The cone of diffuse light was approximately 10 degrees in length.  This cone shaped area of illumination seemed to consist of light reflecting off air particles, similar to the way a flashlight shows a shaft of light when shined into a dusty sky.   There was no noise associated with the light.
 The object and its cone-shaped shaft of light remained stationary for a minute or two.  Then the object moved to the north very slowly until it was due west of me.  Behind the white light (extending south of the light) appeared an area of blue glow approximately 10 degrees in diameter.  The area of blue glow was diffuse and somewhat oval shaped, like a diffuse cloud.  The blue glow was pronounced at first, but slowly began to grow dim.  At this point the white cone-shaped shaft of light that had been emanating from the white point of light had disappeared.  The white point of light grew dim but still traveled northward very slowly.   The diffuse, dim blue “cloud” remained for approximately 10 minutes and then gradually faded.   The white point of light also faded away as it traveled slowly in a northward direction.
 This may have been a rocket launch from Vandenberg Air Force base north of Los Angeles.  However, I am not sure and so decided to issue this report.  I have witnessed a few Vandenberg rocket launches from Los Angeles in the past.   This object, whatever it was, looked nothing like those previous launches.
U. S. Navy missile launch.  PD