As an alternative, if you'd prefer to fish from your boat, you can launch just downstream of the Sandy mouth at Chinook Landing on the Colunbia, and motor up to the mouth. I haven't been there in a while, but the mouth itself often silts up, and makes it difficult to motor up the Sandy, although it may be possible at this time (someone here should know).
NOTE: Once the springers start showing in good numbers, the C at the mouth of the Sandy can get...crowded.