Coin/Self-Service operated car washes are great after those muddy treks (like Truckhaven!).
Keep feeding in quarters, and most now take credit cards, and you can make as big a mess as you want hosing off all the mud, sand and debris.
Most also offer vacuum's for your interior, and brushes to scrape off your rims or undercarriage.
To the right and below are car washes that are either close to our HQ (Dana Point), or along some of the common routes to treks we take (why drive with the mud all the way home!).