Your portal admin URL is like this
https://machine.domain.com/webadaptor/portaladmin
Now you need to find out what exactly machine.domain.com is in your case,
gis1 is machine name, gis1 point to machine where web adaptor installed machine.
victorvilleca.gov is domain.com
So far your URL will becomes to
https://gis1.victorvilleca.gov/webadaptor/portaladmin
Now you only need know your portal web adaptor name, you will be done.
Your portal web adaptor name is 'portal', which you can define during the portal web adaptor post-install configuration process.
https://gis1.victorvilleca.gov/portal/portaladmin
