"Grass Valley Gas" is likely referring to cannabis strains originating from the Grass Valley area in California, such as Grass Valley Girl (a hybrid of SFV OG and Face Off OG) or Skunk G-ass (a potent Indica-leaning hybrid with high THC and a gassy aroma). These strains are known for their euphoric, potent, and sometimes sedative effects, with characteristics like earthy, skunky, and fuel-forward aromas.