the fourth and final step of the staircase.

[keannu]

I think this is a rare structure as "the fourth and final step of the staircase." is usually placed after the subject like "the land" here. Maybe this is a kind of writing style, isn't it?

78gip)A bird's eye view of China would show that China's land descends in four steps from west to east... To the east, the land extends out until it reaches the ocean, the fourth and final step of the staircase. This area includes...

[Raymott]

I think this is a rare structure as "the fourth and final step of the staircase." is usually placed after the subject like "the land" here. Maybe this is a kind of writing style, isn't it?

78gip)A bird's eye view of China would show that China's land descends in four steps from west to east... To the east, the land extends out until it reaches the ocean, the fourth and final step of the staircase. This area includes...

It is placed after a subject like "the land". The subject is "the ocean". The ocean is the fourth and final step. If that is not the intended meaning of the sentence, then it's written wrongly, as you say.

[keannu]

I don't think the fourth and final step of the staircase refers to "the ocean" considering the whole context. If this kind of rare structure is wrong, there is no way to understand it. What do you think?

78gip)A bird's eye view of China would show that China's land descends in four steps from west to east...
The top of this four-step staircase is the Qinhai-Tibet Plateau...
The second step includes Inner Mongolia and other huge plateaus...
The third step is about 500m to 1,000m above sea level...
To the east, the land extends out until it reaches the ocean, the fourth and final step of the staircase. This area includes the tropical southern Ynnan Province. Often called the "kingdom of plants," this area is rare in that it is a tropical broadleaf forest playing host to more than 5,000 plant species.

[5jj]

I don't think the fourth and final step of the staircase refers to "the ocean" considering the whole context. If this kind of rare structure is wrong, there is no way to understand it. What do you think?

The writer was clumsy, that's all. After a slight hiccup, the intended meaning becomes clear. Careful writers avoid causing that sort of hiccup.