/private/var/log/ has all (or most) of the system logs, including system.log. Older rotated logs are bzip2 compressed and appended with a ".#" to the end of their name (ex: system.log.3.bz2).
Other areas of interest include: /Library/logs/, /Library/Application Support/CrashReporter/, ~/Library/Logs/ and ~/Library/Application Support/CrashReporter/
Apps that are sandboxed sometimes have their logs separated from the normal log folders. Check "~/Library/Containers/com.DEVELOPER.APP" and browse to the Logs/CrashReporter folders in those App's sandbox containers.
It's safe to delete the entire contents of any of those folders (not the folder itself), just make sure to Restart and then Repair Disk Permissions afterwards.
You can manually trigger a log rotation by Opening up Terminal and typing "sudo newsyslog -F". I also believe the periodic scripts rotate 1 or 2 logs, try "sudo periodic daily weekly monthly".
All of that aside, you should be able to view the logs in Console:
- Open Console.app
- Click "Show Log List"
- Expand "/var/log"
- Scroll down
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