Wright was 72 years old when he designed Sturges-- at the peak of his career, when his masterpieces of Fallingwater and the Johnson Wax building were under construction, and his experiments with the Usonian concept were taking flight.
In this mature period of his work (his best) Wright was employing several major themes:
-- Organic architecture
-- Efficiency and standardization
-- Advancing technology
Some of these themes were playing out in the Usonian model of building (organic and efficient), while his larger commissions (like Johson Wax, 1935-1939) were pushing the envelope of structural engineering and new forms of modernist design.
The Sturges structure is fundamentally Usonian in its proportions and stylings (architectural grammar), which Wright developed for the Jacobs house in 1936.
But while Sturges is Usonian, it's radical cantilevering (more than any Usonian) and resultant engineering overlaps with Wright's growing penchant for pushing innovation in structural engineering.
Wright, despite his interest in science, didn't think much of formal education generally (he didn't have much) or structural engineers in particular. So, he often ignored engineering input, sometimes disasterously.
At Sturges, L.A. County's Building Department saved Wright from drastically bad engineering assumptions that would have almost certainly ended badly for the house. Wright assumed that timber construction would suffice. L..A. County bulding officials made Wright and Lautner add massive, 2 foot wide steel beams to support the 21 foot cantilever and add steal in several other parts of the structure. The plan revisions have worked remarkable well.