#### Answer

Each base angle has a measure of $55^{\circ}$

#### Work Step by Step

By definition of isosceles triangles, the two base angles are equal. Also, the sum of the three angles of a triangle is $180^{\circ}$
Let $x$ be the measure of each base angle.
$x + x + 70^{\circ} = 180^{\circ}$
$2x = 180^{\circ}- 70^{\circ}$
$2x = 110^{\circ}$
$x = \frac{110^{\circ}}{2}$
$x = 55^{\circ}$
Each base angle has a measure of $55^{\circ}$