I'm not sure. But I think this is a possibility. I checked the three frog species in the area. Western Toad was already eliminated due to their distinctive egg sacs. American Bullfrog was also eliminated due to their habit of laying a huge amount of eggs. Sierran Treefrog and California Tiger Salamander are my best bet. I will provide links below so you can decide. Feel free and entitled to correct me if I'm wrong. I would rather have my first California tiger be an adult than not even hatched yet. But that's just me. :-)
Oh, I also have to add. There are a lot of burrows near and around the swamp so that should help with ID.
Sierran Treefrog:
http://www.californiaherps.com/frogs/pages/p.sierra.html
California Tiger Salamander:
http://www.californiaherps.com/salamanders/pages/a.californiense.html