How long are log files kept?

[Dave Martini 1]

RHEL 3 and 4.
In the syslog.conf file how long are these log files kept and what
is the rotation schedule for instance /var/log/authlog. I don't
see any cron jobs for log rotation.
I need to keep at least 30 days worth of logs.
Thanks much.
Dave Maritni
LLNL

# more /etc/syslog.conf

# Log all kernel messages to the console.
# Logging much else clutters up the screen.
#kern.*                                                 /dev/console

# Log anything (except mail) of level info or higher.
# Don't log private authentication messages!
*.info;mail.none;authpriv.none;cron.none                /var/log/messages

# The authpriv file has restricted access.
authpriv.*                                              /var/log/secure

# Log all the mail messages in one place.
mail.*                                                  /var/log/maillog


# Log cron stuff
cron.*                                                  /var/log/cron

# Everybody gets emergency messages
*.emerg                                                 *

# Save news errors of level crit and higher in a special file.
uucp,news.crit                                          /var/log/spooler

# Save boot messages also to boot.log
local7.*                                                /var/log/boot.log
#auth.info      /var/log/authlog