The figure below shows the telescope limits for the Keck telescopes. In the regions where an elevation limit of ~35° is shown, the telescope hits the Nasmyth deck. Note that this is a problem in the South and West for Keck II, while for Keck I it is more of a problem in the North and East.

Specific limits for the two telescopes:

Telescope Azimuth range Elevations accessible
Keck I 5.3° to 146.2° 33.3° to 88.9°
Elsewhere 18° to 88.9° (unvignetted), 0° to 18° (vignetted)
Keck II 185.3° to 332.8° 36.8° to 89.5°
Elsewhere 18° to 89.5° (unvignetted), 0° to 18° (vignetted)

The lower limit at other azimuths is shown as zero degrees, but in reality there is usually a software limit set at some positive elevation. In certain circumstances this limit may be decreased, to allow access to objects too far south to observe otherwise.

Regarding the upper limits, stable guiding cannot be guaranteed for targets transiting at elevations higher than 84° for Keck I and 86° for Keck II. These limits are orientative and may depend on the instrument in use, since the limitation is caused by the maximum speed the instrument rotator can achieve.