The huge redwood trees in oregon continue to grow tall by

Primary growth.

Explanation:

Most of the primary growth occurs at the tips, apices of the stem and roots. It results in the growth of plant in height.

This is caused as a result of rapidly-dividing cells  that lies in the apical meristem at the root and shoot tip of the plant.

This growth enables the plant to absorb water from the roots and sunlight at the shoots in order to grow.

here, the redwood trees in Oregon continue to grow tall by conducting the primary growth.