In DVD commentary, W. Earl Brown explained why Dan refers to Captain Turner as a "sea creature." In the script he was originally supposed to call Turner a walrus, in reference to his mustache. Brown argued that, given his educational background, Dan probably wouldn't know what a walrus was. David Milch suggested "sea creature" as a replacement and it stuck.
Allan Graf (Captain Turner) and Gerald McRaney (George Hearst) both appeared in three episodes of Simon & Simon (1981) as actors. Allan Graf was also a stunt man in 47 episodes of "Simon & Simon". And of course Gerald McRaney had a leading role in 156 episodes of "Simon & Simon".
When Stapleton is playing with Sara in the bath he pretends her breasts are a communication system on a ship. After Cy leaves the room he resumes and mentions "Iceburg avoided!" Many will be quick to connect this to the Titanic disaster but this is impossible as 'Deadwood' takes place decades before 1912, the year Titanic set sail.