Something is wrong with my dog's face…?

…I was petting him just now and noticed that the left side of his face is bigger than the right. I felt around, and followed up his jaw on both sides. The right side is normal – up the bone, I could feel the tendons, etc. The left side, you go up the jaw and BAM – something hard and circular, about the diameter of a baseball. It doesn't stick out too far, but it is noticible when you hold the skin flat. I'm thinking it's a swollen gland, or something worse. I'm calling the vet first thing in the morning, so I'm not getting pet care online, don't worry. I just need some insight. He is a blue heeler/australian shepherd mix, 2 years old. Male, fixed, and has had no medical problems in his life. Has anyone else had this sort of problem with their dog, and have it turn out to be something… not scary?