What does the letter G mean in a runway identifier?
For runways with other than hard surfaces it is common to list the runways with a letter G for grass or in the case of a seaplane base, with W for water.

An example of this is runway 8G at Boulder (KBDU) and runway 35W at David Wayne Hooks (KDWH).

You can see this information in the Chart Supplement pages and diagrams for each airport.