There's no absolute answer.
I went jogging on the beach the other day and my feet fell about 1 foot into the sand. Then again, some sand is so compacted, cars drive on them (seriously, lifeguards drive their pickups on it)
Also, regardless of the grass, the underlying soil can be clay-like, or well aerated, which will make it softer (don't ask me how I know all this)
If you have a choice and you're spending time contemplating which to choose, I'd say throw a coin so you get to training on not landing on your face :-)