Please create a custom url map source with the following url:
https://mt1.googleapis.com/vt?x={x}&y={y}&z={z}
(just select and copy it) and use it as an offline map download source.
Here is a sample with how custom url map setup looks like:
Please be sure to tell YES to "Use as an offline maps source" and use the url from the file I sent.
Then in offline map download pick that as a "Source".
Alternative map sources.
ESRI satellite imagery for US:
http://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}.png
Open Street Map.
http://a.tile.openstreetmap.org/{z}/{x}/{y}.png
Just copy these sources from here and insert into the custom url map field.
Happy off-roading! Please use star button in the app if you have any problem and I'll be happy to assist!