Walking around with flashlights in salt marshes is generally a good idea, especially right after dark sets in. We have had some luck driving roads that have brackish creeks running along them or bordering salt marshes. Normal time for us seeing them is between 7 at night and 8 or 9 in the morning though last time we were at the beach we found one in a creek a long a jetty that was out at about 12 mid-day. Look for an area with lots of reeds. It takes some time and persistence to find clarkii, but if you can find an area where they have been found, then most likely you will find one pretty soon. And sometimes, they aren't even found too near water. Our first one was found probably half a mile or so from the closest water source. But most of the ones we have seen have been on roads near salt marshes.
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Andy Maddox
Houston Herp Key
The Reptizone