At face value, the poem depicts the American journey which takes them all the way to California's shores, which is as far west as they can go. On a deeper level, the poem depicts the human lifespan. I, a child, very old... the circle almost circled (Whitman 3-4). Line three and four invite readers to take a look at the speaker's life: I, a child, very old meaning the speaker was once a child, but now he is an old man looking back at his life.
The circle almost circled meaning that his time in this world is almost over. Line five to line eight meticulously explained how we, the human race, have been wandered everywhere, done everything, trying to give a meaning to our life. The speaker uses metaphors to point out a question that forever remained unanswered; What is our purpose? We will inevitably have to keep looking for something to give a meaning to our existence.
There is always that need to push forward in us, a strong desire to keep moving; meanwhile, our destination is yet to be known. Now I face home again, very pleased and joyous (9) meaning the speaker is looking forward to his death, and very pleased with the life he had lived. But where is what I started for, so long ago? And why is it yet unfound? (10) Line ten expresses dissatisfaction, Until we find our purpose there is a level of satisfaction that remains unattainable to us, and It creates a sense of incompleteness in us.
Drinnon, Richard. Facing west: The metaphysics of Indian-hating and empire-building. University of Oklahoma Press, 1997.
Jensen, Gregory C., P. Sean McDonald, and David A. Armstrong. "East meets west: competitive interactions between green crab Carcinus maenas, and native and introduced shore crab Hemigrapsus spp." Marine Ecology Progress Series 225 (2002): 251-262.
Storlazzi, Curt D., and Gary B. Griggs. "Influence of El Niño–Southern Oscillation (ENSO) events on the evolution of central California's shoreline." Geological Society of America Bulletin 112.2 (2000): 236-249.