1] Add a "Placemark" (push pin) in the areas of interest and give them meaningful names.
2] Make sure the "Terrain" checkbox is set in the lower-left menu. You can adjust the terrain quality by going to "Tools > Options". Turn off all other checkboxes in the Layers menu, as this would otherwise clutter the scene.
3] Orient your down-view so that the direction you wish to look towards is pointed up (the top of the screen is North (default), West would rotate 90-degrees clockwise, etc.).
4] Open the properties for each placemark and set the view elevation ("Range") properties to about 10-meters height.
5] Using your mouse, click on the upward pointing Compass arrow at the top-right of your view until the Earth tilts so that the horizon is approximately in the middle of the screen.
6] When you're happy with the current view, re-open the placemark at that location, click on the "View" tab, and then click on the "Snapshot Current View". Repeat this for each placemark.
7] From the top pull down menu in Google Earth, click "View > Atmosphere" - an Azure blue gradient will replace the stars in the sky.
Tip: Uncheck the Terrain checkbox before flying to another location. This will allow you to zoom to the next placemark without loading any unwanted terrain mesh.
Since your placemarks are saved, you can then return to them anytime without having to go through the above steps. If you need to adjust the view, then open the properties for any of the placemarks and move the compass with your mouse, then click the button "Snapshot Current View" from the palcemark's properties to save. You can also fiddle with the time of day (Sun icon) in the top of the screen in Google Earth.
Use the above to get a general sense of the area you're interested in. I suppose it's possible to screen-grab images to "stich" a backdrop, you might actually fare better by using the images as a guide for painting.
The 1st view below is of San Bernardino looking North from the SB Depot, the 2nd is Sullivan's Curve on Cajon Pass looking South-West, and the 3rd is Summit looking North.
Have fun!
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