Note that these flowers appear to be protandrous, meaning the anthers mature and dehisce before the stigma opens and becomes receptive to pollen. You can see the whitish remains of the spent anthers (spreading to reflexed) near the top of the fused stamen tube, and the freshly receptive (white, finely papillate) stigmas projecting slightly downward through the top end of the stamen tube. This is somewhat similar to the ''pollen presentation'' mode of typical disk flowers in the Asteraceae. Indeed, the family Campanulaceae is considered a close phylogenetic relative of the Asteraceae.

Postscript (4/26/19): Reference images by Nancy Morin for the two varieties of N. tenuis appear at this link. There can be subtleties in placing plants to variety, since there are often intermediate forms in the spectrum of variation between the extremes of N. t. var. tenuis and N. t. var. aliformis. Though somewhat intermediate, I'd place the plants here as N. t. var. tenuis due to the relatively mildly-zygomorphic corolla shape; the relatively wide & only slightly-curved frontal aspect of the upper two lobes; and the basally white and red-tipped coloration of those upper lobe. As I understand it, N. t. var. aliformis is characterized by a more strongly-zygomorphic corolla shape; with the two upper corolla lobes being significantly narrower (almost linear), more falcate, and more uniformly red throughout. For examples from the Death Valley region, see here and here.