I don't know where exactly the telegraph line ended in Houston but I do know that it went that far (approximately). There are accounts that say that the events of the Battle of Galveston on January 1, 1863, were described in accounts telegraphed live to Houston, making it one of the few battles of the Civil War to be the subject of live news coverage. I recently came across an account by a Massachusetts soldier who claimed that they had cut the telegraph lines before the battle, so either the first account of the news coverage is incorrect or the Confederates managed to restore the line before the battle. Sabine Pass apparentl did not have the direct telegraph connection so after Dick Dowling's victory there in 1863 an officer actually carried the message by train to a place that was connected to Houston. He passed the message along there and by the time the train reached Houston people were in the streets celebrating.